Yeah, I agree. I've wanted to get into home servers for a while now. Te final push was me running a Valheim server for me and my friends on my regular PC while I also recently got some old parts from a friend that build a new PC.
I just needed to gather a few more parts that were missing (case, SSD and CPU cooler) and now it's running like a dream. It's some old-ass hardware: An i5 4460 with 8GB of DDR3 and a 250GB SSD. That's a 10 year old CPU. Doesn't seem like a lot and I haven't put a lot of services on it for now, but it still runs surprisingly well. I'm currently running a Valheim server with often 2-4, sometimes 5 or 6 players are playing at the same time, Adguard and Syncthing. And yet, only 2.4GB of Ram is in use, with often around/less than 10% CPU usage, maybe a little more when a lot of people start playing VH. The CPU temps are around 30-33 degrees celsius today, and that only because summer is arriving. It was consistenly around 25 degrees Celsius past week. Today I tried to add a Wireguard server to it, altough I ran into some problems and I wanted to put some more thought into what OS to run anyway (It's just Ubuntu Server for now as I just wanted to get the Valheim server to run for now).

I'm starting to get into an infodump, but long story short: You can indeed get really, really far with some very cheap hardware. I've only spend around 50-60 euros on it so far, by having some luck, patience and keeping an eye out for deals or viable hardware that people want to get rid of. You can always upgrade to something more powerful or more energy efficient, but just to get into the hobby you really don't need a lot.