Are you looking at Dell/HP/Lenovo’s sites? Don’t do that, those are going to be way overpriced and way overkill. Also most of them are rack servers, not really suited to home use. If anything, you’d want to spec it out as a tower workstation.
Personally I build mine out of parts, and usually used parts. Currently I’m using a little U-NAS NS-410 case, and I replaced all the internals with something better. Total cost was less than $400, I think.