I've got a HKS Hi-Power cat back for sale.
Don't know the mileage, as it came with my car (purchased car at 70,000).
The condition is good, however the flex pipe has been scraped on the bottom side and could possibly need repair.
I never heard any exhaust leak sounds when the exhaust was on the car, so I have no reason to believe that the scraped portion is leaking.
If you are interested, please send me your email address, and I will send you some pics. Looking for $250 + shipping (est $30-50). I'm located in CA.