I've used an old Optiplex I3 540 system with Win7 license ($30) on which was added 16gb of ram bought used ($40) from classifieds ad, and a new GTX 740 ($70).

I've used an old Optiplex I3 540 system with Win7 license ($30) on which was added 16gb of ram bought used ($40) from classifieds ad, and a new GTX 740 ($70). Can play most free games on Steam. Just sayin'.