How much does it cost to run AI features, and how do I keep costs sane?

You pay per token (roughly per word) in and out, so cost scales with usage; a small feature can run on tens of dollars a month while a chat-heavy product can quietly eat 30-60% of revenue. The good news is prices for the same capability keep falling about 10x a year, and three habits (prompt caching, routing easy requests to cheap models, and batching non-urgent work) routinely cut bills 50-80%. Instrument cost per user per feature from day one so pricing decisions are based on data, not fear.

A quick orientation. The real value is below: resources worth your time, from people who've actually done it.