Alternatives to "conventional" Databases?

In his blog post Jakob Greenfield describes how he used the Airtable API as simple alternative for conventional databases to build https://whattotweet.com/ - while still using a conventional code frontend. I was excited by that approach, because databases are usually what eats up a lot initial cost if you build indie projects. Especially if you are just starting with a project and which is not yet validated and you don't make any money from it yet. As far as I know the high database cost is one thing which keeps many people from launching more products. Domains are cheap. But space for databases is comparatively expensive. Long story short: Do you know more alternatives to databases, which are (initially) free or low cost? P.S. You may also check out my short thread on the topic (hopefully a little bit funny and showing gratefulness🤗): https://twitter.com/SamHartmannCom/status/1559981557280022529?s=20&t=Nmk7E4iEUz29LVdb2GbpWw