i literally ( im still sweating from wrestleing the big case ), just packed up a system that i sold for $450 with the following specs:
EVGA X58 mobo
6 gigs corsair 1600 ram
two 1tb WD black drives
corsair 850W PSU
thermalright ultra 120 cpu cooler
i just sold that to a guy for $450, had to haggle tooth and nail to get $450... so that gives you an idea
used computers just arent worth much, especially to people who know what a used computer is worth. the guy i sold tha tto literally has to throw in any current gen graphics card and can play any game at maxed settings, for a total cost to him of about $ 650 - $700.