Hello, I’m having a hard time figuring out how many tokens I would need if I’m building a simple web app that uses a chatbot through the OpenAI API. There are a lot of models available, and I’m not really sure which one to use. The app I’m building is a school project, so I don’t expect many people to use it.

Essentially, the idea is that users would ask the app specific questions, and if they tell the chat to “save” the response, it would call a function to store it.
Also, if I’m testing the responses, would that use up tokens? Or is there a free way to test responses from the API?

I was looking to buy the open air API for my simple NLP classification problem.

Given the current price for chat gpt 4o 2.5$/1 M input tokens I have calculated that it would cost me less than 2$ a month to use the API?

My output is 3 class classification so the output cost is nearly next to nothing.

I feel like something is off..

Does anybody have any real life experience using their API?

EDIT: The answer appears to be "sign up to platform.openai.com instead of ChatGPT, because then you only get charged for the tokens you use, and not the $20/month ChatGPT charge"

Thanks to everyone who answered, I'm up and running, I'll feedback if it starts costing too much!

EDIT 2: Apparently google is too hard for a lot of people, so here's a FAQ for all of those who hijacked this for something else:

1. Just read the docs on the OpenAI integration, it's all there, no hardware required unless you want to talk to it in which case you'll need one of the hardware voice assistants.

2. I'm using it to make my smart home more intelligent - there are loads of examples on Youtube of what people are doing, I want to use OpenAI to do the same thing, so I followed the tutorials on there and got it working

Yes, this is blunt, yes, I think people should share knowledge, but I'm also not going to do your homework for you.

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I don't have the money or the interest to spend on running a local LLM, so I want to run hosted.

I've noticed the OpenAI API is billed "per million tokens" rather than ChatGPT which is billed at $20USD/month, so I'm starting to work out how much it will cost me to run OpenAI as the backend for my HA setup.

Please note that I am only interested in hearing from people who are already running OpenAI with HA - if you're not doing this, I'm sure your project is awesome and if this doesn't work then I'll definitely be interested in what I should use instead, but right now I need this specific question answered.

Thanks in advance for your time!