Very small forum and just 8 users using daily Discourse AI and around 20’ish the chatbot. DAI creates few images every day and creates perhaps 5 longer texts and chatbot answers to short questions. Mostly DAI uses 3.5-turbo but now 4 turbo, the chatbot is under 3.5-turbo-16k or what the exa t model now was.
It costs to me quite close to 50 USD a month now. To compare VPS costs… 24 or so EUR and S3 something like 15 USD. So that wise OpenAI os quite expensive and I did an error when I introduced GPT models to my active users 
And I really really really much would like to get group restrictions what model they can use.
For bigger communities free-to-all GPT can be really expensive.