While using desktops for this has sometimes been nice, the big things I want out of a server are
- low power usage when running 24/7
- reliable operation
- quiet operation
- performance but they don't need much
So I've had dual Xeon servers and 8-core Ryzen servers but my favorites are a miniForums with a mobile Ryzen quad core, and my UGREEN NAS. They check all the boxes for server / NAS. Plus both were under $300 before upgrades / storage drives.
Often my previous gaming desktop sells for a lot more than that ... I just sold my 4 year old video card for $220. Not sure what the rest of the machine will be used for, but it's not a good server because the 12-core CPU simply isn't power efficient enough.