Choosing an API as an individual developer: work backwards from monthly usage

Do not compare prices yet - estimate usage first

Most people pick in the wrong order: price first, usage later. But without usage there is nothing to compare. The difference between a 0.3 rate and a 0.8 rate is ten CNY when you spend 20 CNY a month, and a thousand CNY when you spend 2,000.

Step one: estimate monthly token usage

Three reference magnitudes (real usage varies widely; these are only a starting point):

RAG applications push input volume up sharply - every request carries a batch of retrieved documents.

How to estimate: connect to any site, use it for a week, then export the usage records. That is the most accurate method.

Step two: pick a model from the usage

Step three: trade-offs on a tight budget

An individual developer's resources - money and time - are both limited, so be explicit about what can bend.

What can bend: the rate, the payment method, support response time.

What cannot:

• Protocol compatibility - if it is incompatible you simply cannot use it; there is no middle state
• prompt caching support - this can be a several-fold cost difference, larger than the rate itself
• Your balance not walking away - every yuan you top up can be lost

Three practical suggestions

One: top up small, and test several sites side by side.

The most common loss for an individual developer is not "the unit price was 20% high" but "I topped up 500 and the site vanished". So never top up more than one month of actual usage, and run two or more sites in parallel for the first two weeks.

Two: prefer sites that can issue an invoice.

Even if you personally do not need to expense it, it is a useful filter: being able to invoice implies a properly registered entity, and walking away costs it far more than it costs an individual.

Three: do not spend two hours to save 10%.

Individual developers routinely overestimate the money saved and underestimate the time spent. If two options differ by 30 CNY a month, take the one that is simpler to configure.

A process you can use directly

1. Connect one site and run it for a week, then export usage  -> your real token mix
2. Work out the theoretical cost from that mix               -> your personal cost formula
3. Compare 2-3 sites side by side                            -> using the formula, not the rate
4. Pick one primary and one fallback                          -> never only one
5. Reconcile on the last day of every month                   -> check actual against expected

Step five is the one people skip most, and it is the one that determines whether you actually understand your costs.

Related reading

• From list price to your invoice: a worked cost conversion
• Prepaid, subscription or pay-as-you-go: where each billing model wins
• Six signals that a relay service is about to disappear