I just picked up a pair of X3's for $60 + shipping. Not that I actually wanted the games - at that price I got an arcade PC case with PSU, GT660, hard drive mounting plate and a JVS/fastio card - the dongle, original HDD & the PCB can go in the bin for all I care.
I'm putting a M-ATX motherboard, i7-3770 cpu, 8Gb ram and a 250Gb SSD inside instead. I work in IT so have plenty of Windows 7 PRO COA's available so they make perfect MAME PC's (Just need the drivers for the JVS card so I can use them in the Vewlix without using a JVS-PAC.