You're right that this stuff isn't cheap. I'm running https://Docalysis.com/ (a chat with files website) which has expenses growing every month, so you need to make sure your price is above what it costs you, and can't give everything away for free.

His product gives you a few thousand tokens for free, then makes you add your own OpenAI API key after that, so that he isn't paying for the chat responses from then on.