Yes, that should work well with Retool. You just need to build the app in Retool, and then enable "public applications", which'll let you expose the app publicly. We don't bill for public users.

(Theoretically, the end users could get all the data by inspecting the network requests. But there's really no way around that given that you're exposing the app and its data publicly. I suppose you could get around it by adding a password to the public app. LMK if you need help with that!)