Mac Mini (M1 and later) under Asahi Linux just uses 5 W for a normal workload. If you push it to 100% of CPU it reaches 20 W. That’s very little.

Only thing is you can't run Proxmox which makes self hosting much better, and you'll be limited to ARM builds, which on server is at least a lot easier than trying to run desktop apps. Modern micro desktops are also fairly power efficient, perhaps not quite as low as the mac, but much lower than a regular gaming desktop idling.

Avoid stacking in too many hard drives since each one uses almost as much power as the desktop does at idle.

I doubt anyone who is too tight on cash that they have to think about the electricity cost of a home server can afford a Mac.