Ask HN: How to setup back end for a side project most effectively?

Hey, I'm a college bachelor and I'm building a simple web app concerning high-school contests. Most of the work will be done at client-side, but I'd like to have some features that will depend on a server.

Concretely I'd like to have:

- Database of users and also of the items that will constitute the main content of the site (comparable to an e-shop items database, but without pictures)

- Sending notifications to a user when some other user does something

I think the number of users will be in the hundreds at most. How do I set this up to spend as little as possible? I know of Azure and AWS and similar solutions, but their sites are so complicated that I don't even know whether they're the right tool to solve my problem, not mentioning the question if they're the _best_ tool. Thanks for any help!