What’s the easiest way to convert some excel spreadsheets into an API and where do I host it?

You can deploy it to firebase or put it on GitHub as a repository. If you put it on GitHub, you can use GitHub pages to provide an API endpoint or just using the raw file on GitHub

Convert Excel to CSV as I mentioned before, and then u can use one of the following tools to convert it to JSON:

Afterwards, create a GitHub repo on or firebase app, then deploy it.

If you’re doing it from code, there are packages for NodeJs and Python-like the ones below that can help with the major task: