Your probably not going to get 500+ for it just because of that fact that there used parts, your not a brick and mortar store with a warranty, and did i mention there used parts. People, especially non-tech people, would rather spend 700 and get a warranty than 500 and cross their fingers. I would say the max you could get for that would be 300-350, but that shouldn't keep you from asking 500 off the bat, just be prepared to take lower.
Thanks so much for your input. That is very helpful. I don't know if it makes a difference but all the parts are new and never been used. I actually still have the boxes for the HDD, case, blu-ray drive, card reader, and the remote. The other parts were bought as "used" but never installed. I was also thinking of offering a 30 day warranty. Does that change anything?