Assuming everything is lightly used, I'd peg the CPU at around $75 (it's somewhere in the neighborhood of 80-100 new right now), the mobo at $50-75 (this is assuming it's a micro-atx, I couldn't find that exact model online, but similar model numbers appear to be generally micro instead of full ATX, which might be worth a little more).
Taking into consideration ~20 bucks worth of RAM, a case of unknown quality, and a used (although decent brand) PSU, I'd guess the whole package could be something around $150 or $200
For comparison's sake, Newegg had a 'shell shocker' yesterday with an Athlon X2, micro-atx motherboard with onboard GPU, 2GB of RAM, 1TB hard drive, case and PSU (no optical drive, if I recall correctly) and the entire deal with brand new components was $200. I think it was around a $50 savings from the regular price. Your quad core proc is certainly better, but less RAM and no HD counts for something too.
Hope this helps!