Looking for a good CMS for a mobile app

I have a simple mobile app that is using Firebase Realtime Database, but the more data I have, the more difficult it is to manage, moderate and update the entries.

I was testing some alternatives like Contentful* Strapi and most recently Cockpit headless CMS. They all fulfill most of my requirements but have some serious issues as well:

- Contentful is fine, but as it's very expensive as soon as you want to add second workspace. I don't wont to violate the terms of use by creating another account.

- Strapi has similar issue as above and it requires Docker container or VM. If possible I'd like to limit this to something simpler like basic web hosting.

- Cockpit works really nicely on my basic web hosting, but it's missing some basic documentation

What would you propose to try out as a basic CMS that would:

- provide a graphical UI to import, manage and edit the data

- expose RESTful API to fetch and edit the data

- be relatively secure

- inexpensive (few $/month top)

- be self-hosted on basic web hosting or Heroku/DigitalOcean/Netlify instance