I bought an older Dell from eBay that had WinXP loaded with the port to run Mach3 and serial port for my Emco machines, runs other programs without trouble, clearly best not to have it connected to the net but for a workshop computer it works fine.

Cost I believe was around £60 which included a wired mouse and keyboard + flat screen monitor.

Emgee

I also got a reconditioned XP machine from ebay , about £50 and just use that for the CNC Though I can use a USB for Mach3

The Breakout board on the CNC has a USB Socket rather than a parallel.

If you use the uc100 for motion control the demands on the PC are minimal.  I replaced my old XP machine with a Dell mini about the size of a cd case but thicker and it works perfectly fine.  I’m running Win10 with no issues.  Not a good idea to scrabble round for an old xp machine with parallel port, you’ll only have to replace again.  I found I needed only minimal reconfiguration of Mach 3 with the uc100, mainly to increase the pulse rate.  Machine also has WiFi and serves as a general purpose workshop computer.