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Local inference · Cost Structure · Open Models · Apple Silicon · Cost ComparisonTool of September 2026, prices read 12 October 2026

What local AI actually costs

Forty-Three Years Was Last Month’s Price

A one-page calculator asks how long a machine bought to run open models locally takes to pay for itself against renting the same model by the token. On its default settings — a $3,499 Mac Studio, a 27-billion-parameter model, half a million tokens a day — it answers 43.6 years, and the answer travelled. The number is sound: it publishes its data and its formula, and every one of the thirteen figures in the coverage recomputes exactly. What the number depends on is the interesting part. Make the machine’s electricity free and it moves by under four per cent. Change which of twenty live hosts you rent from and the same machine, the same model and the same day give anything from 19 years to 183.

The arithmetic checks out; the date on it does not What the tool says, what reproduces from its own files, and what has changed since those files were written.

  • 43.6Years to break even, on the tool’s published default settings
  • 13 / 13Published figures that recompute exactly from the project’s own data files
  • 0 / 98Measured speed rows in its data that cover the machine in that default
  • 19 – 183Years to break even across the 20 hosts serving that model today
  • 3.8%How much the answer moves if the machine’s electricity were free
StandingWhatWhere it is established
ConfirmedEvery figure in the coverage — the monthly bill, the electricity, the saving, the memory, the speed, the waiting time, even “27 of 39 models fit” — recomputes exactly from the project’s own data and its own published formula.Four data files and the formula, all published in the open. Recomputed here on 12 October 2026.
ConfirmedThe prices behind that answer were checked on 3 September 2026. Queried live today under the tool’s own rule — the cheapest active host — the same workload costs about a quarter as much, which pushes break-even to roughly 180 years.The data file records the rule and the date; the marketplace’s own API was queried on 12 October 2026.
ConfirmedTwenty hosts serve that model right now. Input prices span 25-fold and output prices 3.5-fold, so break-even on one machine, one model and one day runs from 19 years to 183.All twenty endpoints and their prices, from the marketplace’s own API, 12 October 2026.
ConfirmedThe machine in that default has no measured speed anywhere in the project’s 98 measurements — it had not shipped when the data was compiled — and the project says so itself.The measurements file, read row by row, and the project’s own list of known gaps.
Confirmed, but not verifiable hereThe author’s own summary: at a million tokens a day the quickest payback in that capability class is 8.3 years, and it drops under a year only at around 20 million tokens a day.Written in a public forum thread on 15 September 2026, against prices checked twelve days earlier.
UnconfirmedWhether any of today’s cheapest prices are introductory. A 25-fold spread on one model invites the question, and nothing in the marketplace data answers it.Twenty endpoints are listed as active; nothing distinguishes a standing price from a promotional one.

What the number is

A correct calculation, on stated assumptions, from data checked on a stated day, by a project that publishes all three and lists its own gaps.

What it is not

A constant. Two of its inputs move it by a factor of ten or more and both have moved since; the two that look decisive — the machine’s speed and its power — move it by less than five per cent between them.

Thirty-nine days from the price check to the price The data was compiled before the machine it describes went on sale, and the figure reached a new audience four weeks later.

  1. 12 Mar 2025A research group publishes the trend the whole question turns on: the price of a given level of capability has fallen steeply and repeatedly, by as much as 40-fold a year on one benchmark.
  2. 3 Sep 2026The project records its prices and defaults as checked. The model in the default is priced at $0.32 in and $2.50 out per million tokens, by the rule “cheapest active endpoint”.
  3. 15 Sep 2026The calculator is posted to a public forum. It draws 47 points and 99 comments, and the first of them refuses the premise: privacy, the commenter writes, makes it pay off instantly.
  4. 22 Sep 2026The machine in the default setting ships — nineteen days after the data describing it was compiled. Its speed in the calculation is an estimate from memory bandwidth, and is labelled as one.
  5. 11 Oct 2026The figure is reported to a Chinese-language audience, twenty-six days after it was published and thirty-eight days after the prices behind it were read.
  6. 12 Oct 2026The same model’s live prices are read across twenty active hosts. By the tool’s own rule the workload now costs about a quarter of the recorded figure, and the twenty prices do not agree with each other either.

Four inputs, and only two of them matter Each row below moves one input and leaves the rest at the published defaults.

The formula is published, and reading it is most of the work. The cloud side is charged for input and output tokens. The local side is charged for the electricity burned while generating output — no idle draw, no time spent reading your prompt, no depreciation, no share of the machine’s other uses. Whatever else that is, it is not a calculation rigged against buying the machine: on running costs it is as generous to the local box as arithmetic allows, and the hardware price is left doing all of the work.

Which is exactly why the local side of the equation barely moves the answer. At the published defaults the electricity is 3.8% of the cloud bill, so the two numbers that look like the local machine’s whole story — the speed and the power draw — have almost nowhere to go. Halve the speed and you add fourteen months to forty-three years. Quadruple it and you take fifteen months off. Make the electricity free and the answer is still 42 years.

That reframes the project’s most-quoted caveat. Its data holds 98 measured speeds and none for the machine in its own default, which had not shipped when the file was written; the project says so in its list of known gaps. It is a real gap and it decides the time cost completely — the forty seconds a thousand tokens, the quarter-hour of extra waiting a day. It decides the money almost not at all.

The two inputs that do decide it are the API price and the volume. On the volume: the default is half a million tokens a day, and the answer is a fact about that number. Three years’ payback needs 7.3 million tokens a day and one year needs 21.8 million, both inside the machine’s own published ceiling of 34.6 million. The author says the same thing in his own words — under a year “if you’re running agents at around 20M tokens/day”. On the price: see the next section, because one number cannot carry it.

  • 3.8%The electricity, as a share of the cloud bill it is meant to beat
  • 42.0Years to break even if the machine ran on free electricity
  • 7.3MTokens a day needed for a three-year payback, against a default of 0.5M
Move one inputBreak-evenAgainst 43.6 years
Speed estimate halved, 25 to 12.5 tok/s45.4+4.1%
Speed estimate quadrupled, 25 to 100 tok/s42.4−2.8%
Power draw doubled, 145 to 290 W45.4+4.1%
Electricity at the official current figure, 18.31¢43.8+0.3%
Electricity free, 0¢/kWh42.0−3.8%
API price: cheapest live host today182.9+319%
API price: dearest live host today19.1−56%
Usage at 7.3M tokens a day3.0−93%
Usage at 20M tokens a day1.1−97%

“The cloud price” is not a number Twenty hosts, one model, one day, and the break-even each of them implies for the same machine.

Price band, per million tokensHostsThis workloadBreak-even
Cheapest: $0.040 in, $1.350 out2$1.85/mo182.9 yr
Under $4 a month9$1.85–3.9279.6–182.9 yr
$4 to $10 a month9$5.09–9.4631.7–60.3 yr
Over $10 a month2$14.46–15.5419.1–20.5 yr
The figure in the calculator, checked 3 Sep—$6.94/mo43.6 yr
  • The switch nobody mentioned

    43.6 years is the kindest answer available

    Off by default

    • The tool carries an option to let API prices keep falling. It is switched off by default, so the headline holds today’s price flat for forty-three years.
    • Its own note: prices “have not behaved that way”, and switching the option on “pushes break-even out”.
    • Past a point, the note says, “the API costs less than your electricity” and break-even “stops being reachable at all”.
  • What it leaves out

    And says so, item by item

    From the project’s own files

    • The whole purchase is charged to inference. Nothing is credited for video work, compilation, or anything else the machine does, and nothing is amortised against resale.
    • The power figures for the 2026 machines are stand-ins, because the maker has not published any; every affected row is flagged.
    • The daily ceiling treats reading your prompt as costing no time. Its own note: the real ceiling is “plausibly 20-30% lower”.
  • What it cannot price

    The first reply refused the premise

    A public forum, 15 September 2026

    • “It pays off instantly, because [the vendors] can no longer see what I’m doing… If I am offloading some of my thought processes to a machine, I want to own that machine.”
    • A second reply makes the methodological point in the tool’s favour: the fair comparison is a host running the same open model, which is what it does.
    • Offline stability, no change of terms, no change of price and no content rules are in the same category: real, and not expressible in dollars a month.
Also worth knowingDetail
A dated figure is not a wrong oneThe calculation records the rule it used and the day it used it. A price that moved afterwards makes the figure old, not false — and this is a field where a figure can be old in five weeks.
Cheapest is a rule, not a hostThe data file records the rule and the date, never which provider it landed on, so the September figure and the October one cannot be traced to the same host.
The price spread is a question, not a recommendationNothing here tested latency, throughput, data retention or reliability at any of the twenty hosts. A 25-fold spread on one model is a reason to look, not a reason to pick the bottom of it.
What could not be readThe maker’s own purchase page confirms the prices of the memory tiers either side of the one in the default, but draws the configuration prices with script, so the $3,499 rests on the project’s data file and the source it cites.

Which way of buying inference suits which buyer The calculation answers one question well. It is not the only question, and it is not the same question for everybody.

  • Rent it

    If the bill is the reason

    Half a million tokens a day or fewer

    • Best at: costing nothing up front, never being the wrong machine, and getting cheaper while you sit still.
    • At this usage the bill is a few dollars a month, and the hardware would need decades of them.
    • The trade-off: your work goes to somebody else’s machine, and the price, the terms and the model can change without you.
  • Buy it

    If the volume is already there

    Millions of tokens a day, every day

    • Best at: turning a fixed cost into unlimited use. The machine does not charge by the token, so the heavier the day the better it looks.
    • Three years’ payback at 7.3 million tokens a day, about one year at 20 million — both within the machine’s own ceiling, and both a long way above the default.
    • The trade-off: it is slower per token than a data centre, and the hosted price you are beating is falling underneath you.
  • Buy it anyway

    If the reason was never the bill

    Confidential work, or no network

    • Best at: the things no calculator has a column for. The work never leaves the room, the terms cannot change, and it runs with the network down.
    • Where confidentiality is a legal requirement rather than a preference, the break-even question does not arise at all.
    • The trade-off: be honest that this is what you bought. The arithmetic above is not an argument against it, and it is not an argument for it either.

Settled

The arithmetic is right and reproducible from published data. At half a million tokens a day the machine does not pay for itself on the bill, by a wide margin, and the margin is not sensitive to anything about the machine.

Open

What the hosted price will be. It fell by roughly four times in thirty-nine days on one reading, twenty hosts disagree with each other by 25-fold today, and the trend the tool cites is from an analysis its own note says predates this year.

Hold this loosely

Any single break-even figure, including every one on this page. They are all snapshots of a price that moves weekly, computed at a usage level somebody chose. Re-run it with your own two numbers; the rest barely matters.

  • Work out your own two numbers before anything else: tokens a day, and the price of the host you would actually use. Together they move the answer by a factor of ten or more. The machine’s speed and its electricity move it by under four per cent between them.
  • Check the date on any break-even figure, including this one. The prices behind the headline were five weeks old when it reached a new audience, and the workload they describe had changed by about four times in the meantime.
  • Price the host you would use, not “the cloud”. Twenty of them serve this one model today and their input prices differ by 25-fold. Which one you pick changes the answer more than anything you could buy.
  • If you bought the machine for privacy, say so and stop doing the sum. The calculation charges the whole purchase to inference and credits nothing for anything else the machine does. It answers a question about money; it was never the question you were asking.

Quick notes

  1. Explainer · prices read 12 October 2026

    Does local AI pay for itself?

    How the Sunk Cost calculator works, the ideas behind it, and what its number really depends on.

    For beginners and practitioners1 / 16

  2. The question

    Buy a machine, or rent the AI by the word?

    Buy: run it at home

    Pay once for the hardware, then only for electricity. Like buying a car.

    Rent: use an online API

    Pay a small fee for every piece of text the model reads and writes. Like taking a taxi.

    The one question

    How long until the purchase earns back its price?

    2 / 16

  3. The tool

    Sunk Cost is a free, open-source pay-back calculator

    Built by one developer to test a popular claim: buy a Mac, run models locally, and it pays for itself. Its README says what it is for: “It is willing to say ‘this doesn’t pay off’. That is the product.”

    • 39current open models, of 55 in its data
    • 56machines: Macs, graphics cards and more
    • 15 Sepposted to Hacker News, 2026

    The data, the formula and the gaps are all published3 / 16

  4. The headline result

    43.6 years to pay back a $3,499 Mac

    A Mac Studio with the M5 Max and 64 GB, running Qwen3.8 27B, at 500,000 tokens a day. The saving is only about $0.22 a day.

    • 43.6years to break even, on the published defaults
    • 13 / 13published figures that recompute exactly
    • 3 Septhe day its API prices were checked

    Correct arithmetic, on prices from a stated day4 / 16

  5. Concept 1 · Tokens

    AI reads and writes in tokens, and you pay per token

    What is a token?

    A small piece of text, often part of a word. Models count, and are priced, in them.

    Input and output

    Input is what you send: the question, files, chat history. Output is what the model writes back.

    Price per million

    As the tool recorded it on 3 September: Qwen3.8 27B at $0.32 per million input and $2.50 per million output. Writing costs more than reading.

    5 / 16

  6. The method

    The whole calculation is three steps

    1. 1Daily API billinput tokens × input price + output tokens × output price
    2. 2Daily electricity at homehours spent writing output × machine watts × electricity price. Nothing else on the local side.
    3. 3Break-even daysmachine price ÷ (API bill − electricity). If the saving is zero or less: never.

    The formula is published in the project’s README6 / 16

  7. Worked example

    Walking the default to 43.6 years

    StepCalculationPer day
    API input468,750 tokens × $0.32 per million$0.150
    API output31,250 tokens × $2.50 per million$0.078
    Home electricity0.35 h × 145 W × $0.17/kWh$0.009
    Saving0.228 − 0.009$0.22
    Break-even$3,499 ÷ 0.2196 = 15,936 days43.6 yr

    Electricity barely counts

    It is 3.8% of the API bill. The 145 W is the project’s own stand-in, because Apple publishes no power figure for the 2026 machines; make the electricity free and the answer is still 42 years.

    7 / 16

  8. Concept 2 · Memory bandwidth

    Home speed is limited by how fast memory can be read

    To write each word, the machine re-reads the whole book. A wider pipe, or a thinner book, means faster writing.

    • 614 GB/smemory bandwidth of the M5 Max
    • 18.6 GBread per token: weights plus KV cache
    • 24.8 tok/s614 ÷ 18.6 × 0.75 efficiency: an estimate
    • 0 / 98measured speed rows that cover any M5 machine

    8 / 16

  9. Concept 3 · Context window and KV cache

    Long chats need more memory, and run slower

    Context window

    How much text the model keeps in view at once, such as 32k tokens. Its short-term memory.

    KV cache

    Notes the model keeps on every token it has read, so it need not work them out again. They grow with every token: 2.15 GB at 32k for this model.

    The fit test

    Weights plus KV cache must fit in usable memory. A 64 GB Mac offers 48 GB to the GPU, and 27 of the 39 current models fit at 32k.

    9 / 16

  10. Concept 4 · Prefill and decode

    Reading a prompt is fast; writing is slow

    Prefill: reading

    The whole prompt is processed at once, in parallel, limited by raw compute.

    Decode: writing

    One token at a time, re-reading memory for each, limited by bandwidth. Tens of tokens a second at home.

    The simplification

    The tool times decode only and treats input as free. Its README says the real daily ceiling is plausibly 20–30% lower on input-heavy work.

    10 / 16

  11. Concept 5 · Prompt caching

    Re-sent text is often billed at a steep discount

    When the start of a prompt matches one the provider saw recently, it reuses its stored work — a cache hit — and charges less for those tokens.

    ProviderCached input, against the normal price
    OpenAI0.25–0.50×
    Gemini, Moonshot AI0.25×
    DeepSeek; Alibaba Qwen, when asked for0.1×

    Not modelled

    Sunk Cost charges all input at the full price. For agents that mostly re-read their context, renting is cheaper than shown, so pay-back is longer still.

    Cache prices as OpenRouter lists them, read 15 October 202611 / 16

  12. What changes the answer

    Usage moves the date, not the finish line

    • 436 yr50,000 tokens a day: light personal chat
    • 43.6 yr500,000 tokens a day: the default
    • 13 months20 million tokens a day: agents around the clock

    The finish line

    The machine is worth about 8 billion tokens of saved API spend. Use it faster and you reach that line sooner. Falling API prices push the line further away.

    Default Mac Studio with Qwen3.8 27B, prices of 3 September12 / 16

  13. The price under the number

    “The cloud price” is not one number

    Twenty hosts serve this model. Same machine, same model, same day, priced on 12 October:

    API priceThis workloadBreak-even
    The tool’s recorded figure, 3 Sep$6.94/mo43.6 yr
    Cheapest live host, 12 Oct$1.85/mo182.9 yr
    Median of 20 live hosts$5.24/mo58.5 yr
    Dearest live host, 12 Oct$15.54/mo19.1 yr

    Old, not false

    By the tool’s own rule — the cheapest active host — the answer 39 days later is closer to 180 years than 44. The switch that lets API prices keep falling is off by default, so 43.6 is the kindest answer the defaults give.

    13 / 16

  14. Reception

    The press repeated the number; the community challenged it

    Media

    The 43.6 years travelled, reaching Taiwan’s TechBang on 11 October, nearly four weeks after launch.

    Hacker News

    The speed estimate is “at least 2x” too low; it pays back fast at 24/7 use; privacy matters more than money.

    The author’s changes

    A field for your own measured speed and a best-buys page, both on launch day; on 18 September the usage slider was raised to 100 million tokens a day.

    14 / 16

  15. Limitations

    What the calculator leaves out, and which way it pushes

    Left outIncluded, home hardware would look…
    Resale value, other uses, privacybetter
    Speculative decoding, MTP, 8-bit KV cachefaster, but the saving barely moves
    Many agents batched on one machinebetter, at very high volume
    Prompt-caching discounts on the APIworse
    Prefill time, idle power, depreciationworse

    15 / 16

  16. Takeaways

    Buy for privacy or heavy agents, not for savings

    • Use your own two numbers. Real tokens a day from your provider’s dashboard, and the price of the host you would actually use. Together they move the answer tenfold or more.
    • Enter a measured speed, from llama.cpp or vLLM, rather than trusting the estimate — it decides your waiting time, if not your bill.
    • Discount for caching. Agentic work with many cache hits makes renting cheaper still.
    • Check model quality. The tool compares open models; a frontier subscription is a different trade-off.

    The calculator: sunkcost.ai16 / 16

  • the report of the calculator in TechBang, 11 Oct 2026
  • the calculator itself at sunkcost.ai, and its repository — the README carrying the formula and the list of known gaps, and the four data files for hardware, models, defaults and measured throughput
  • the Show HN thread of 15 Sep 2026, for the author’s own figures and the first replies
  • OpenRouter’s models and endpoints APIs, queried 12 Oct 2026 for all twenty live prices
  • Apple’s Mac Studio specifications and purchase pages
  • Epoch AI, ‘LLM inference prices have fallen rapidly but unequally across tasks’, 12 Mar 2025
  • and the US Energy Information Administration’s Electric Power Monthly, via its API. All read 12 Oct 2026. The slides also draw on OpenRouter’s prompt-caching guide and the repository’s commit history, both read 15 Oct 2026.

Reliable

Reliable, but with an interestWorth believing and reliableWeak on both, and used with careHonest, but thin

Worth believing

Each point is one source used, placed by two judgements on a six-step scale. Points carry no names: the chart shows the shape of the evidence, not a verdict on any publisher.

Versions

This document is rewritten when what it says has to change. Every version stays published at its own address.

  1. v0002 current
  2. v0001 superseded

The current version is also at latest/.