I need a quotation for openai api credit

This is as long a piece of string. There are many variables. The more you use it, the more reasoning you require, the more images you process, the bigger the model you use the more tokens you use, the more it will cost. My suggestion is purchase a small allocation of credits and experiment to see what budget you need longer term. Another solution if you are just using AI to write code consider a ChatGPT subscription and you can authenticate with that to use your token allocation that comes with that subscription for many of the official tools, e.g Codex-CLI.