I bought recently used Workstation HP Z600 from year 2010 on ebay. link
It cost less than 300 Euros and this is Mercedes of computers! Everything solid as rock. These machines were very expensive as new.
I got 2 xeon 4-core E5630 80w processors, 8gigs of ram, Quatro 4000 graphic card which still costs over $100 on ebay and Windows 7 Sticker.
I removed to trash existing 8gigs of memory (2gb modules) and added new 6x4gigs DDR3 ECC server modules and I paid for it just $50. Link
Wow! 24gigs of ram for just fifty bucks (machine limit is 48 gigabytes). Server memory are very cheap.
With 2x 2.53ghz Xeons (2.8ghz turbo) this system rocks! its faster than current top i7 processors, and whole machine costs less than comparable processor :)
I get 30.000 mips in 7zip benchmark while i7-7700K gets the same score.
But I can buy on ebay two much more powerful 6-core xeon core processors Xeon X5670 with total 24threads just for $100 for pair which increase performance almost twice!. Link This is bargain!
People don’t know that these Xeon Workstation are so cheap and so powerful.
And guest what, this computer accepts and recognizes old PCI 5V Sound Cards like Motu 424 or even Yamaha YMF724 with hardware opl-3 chip :) You can use it for old FM trackers or games in KVM in Linux with DOS/Windows98 Virtualization PCI-passthru tehnology