i paid 300 out the door including tips... 500 is FAR to much... you can buy custom made parts for cheaper than that.
buy a gt take off cat back and a pacesetter adapter, cut and weld in the adapter so you can bolt up the cat back, this should run you 100 for take offs and 30~ for the dual adapter (this will alow you to unbolt the cat back if need be, this is a good idea....) then if you want new muffers buy em, add up 130 + mufflers + labor for welding in the adapter and mufflers.