i was getting annoyed not knowing how much gpt3 / gpt4 was costing me this past week so I did some digging around and found out that OpenAI has an API which reveals usage info!
I then went ahead and made a dashboard for myself to monitor the usage :). You can use it for yourself here https://llm.report
Let me know if you have any suggestions or feedback
p.s. your API keys are stored in browser only