What site? I've never seen them on sale before.

I have 2, I've got a 4b which I got to build a little NAS with, but my last place wasn't a fan of that idea so it never happened. Currently not in use.

I also have a zero W I got recently to run a lightweight python script that just archives a webpage once per day into the Wayback machine. In the future, I'll probably use the 4b either for a more complex archiving script (I discovered a nice CLI utility with a lot more features than the one I made), probably run on some sort of Cron job and possibly modify it to be easily configured remotely from any device, rather than just SSHing.

I'm going to use the 4b to run a local ArchiveBox instance and a Tube archivist instance to archive some YouTube channels eventually.

Once you find your niche, you can do pretty much anything with it. My niche is archiving and datahoardery, so anything like that will probably run on one of my pis at some time in the future