OpenRouter.ai does this pretty well. It has a pretty reasonable flow. It supports enough free models that you can do at least _something_ without a person havin

OpenRouter.ai does this pretty well. It has a pretty reasonable flow. It supports enough free models that you can do at least _something_ without a person having to pay anything (even if quality is a bit iffy). They have user-set spending limits, and each key is bound to the service. Their privacy policies seem decent. The other option is Gemini, which has enough free credits to really be free for any small app. Unfortunately you can't use that through OpenRouter, you need your own developer account to be able to take advantage of Gemini's free offering.