If you've got Gamestop credit to burn, a used copy comes down to $37.79 after CAG16+Edge. After free shipping+tax it would probably be a bit more, but if you're looking to get rid of some credit, that isn't bad.
Alternatively, you could get Ratchet and Clank and $56 in other items to qualify for 25OFF. In a best-case scenario you'll save $16.25 on Ratchet and Clank (bringing it to $33.75 used) and about $13 on your other items (depending on whether you get new or used.) But, of course, you have to be able to throw down at least $71 to qualify. :] Hope this helps someone out.