i see workstation graveyards in closets and garages that would make perfectly good white box servers.. yeah theyre retail shit that mostly lack the 'always on' resilience of server level hardware, but a dedicated box for a server process is always better than a shared user/server environment.
youd prolly be hard pressed to find any old shitty retail box that you couldnt slap a nix variant.
keep good backups.. in my experience, hardware dies in this order: spinning drive, power supply, motherboard