CPU: $90.00
RAM: It's DDR3...$20.00
HDD: $26.00
SSD: $10.00 to $30.00
PSU: If it's crappy, you'll be replacing it...$25.00
MB: $70.00
GPU: $88.00
COOLING: $50.00
It's probably been ridden hard, and the PSU will be suspect from the get-go. Don't expect much from the SSD, either.
I'd say that a high offer would be something like $389.00, but I wouldn't feel comfortable offering more than $300.00 if my wallet was involved.
If the haggling took it over $340, I'd walk.