Depends on what you want to use it for but I have a six core CPU a 750 watt power supply , have a fair amount of RAM like 8 Gig at least. Don't chince on the mother board and get a descent video card. figure about 120 bucks for mother board and roughly 150 - 250 for video card Nvidea. Alot of times depending on where you live someone builds them for about 100 bucks but you save that in cost if they are worthy of their salt.
6-700 750 extra fans and case for a descent system. maybe less. Good luck. D