I got mine built from stock dump-pipe back for $750(mild steel) inc mandrel bends with straight thru muffler.I then purchased the Aussie dump-pipe(worthy mod for spool)
All it is, is a straight 3inch pipe from the down-pipe to a flexi section then to rear axle. Then it requires the mandrel bends and muffler etc. Mind you I don't have a cat installed so that brought the cost down.
Apexi, Blitz, HKS and Aussie Exhausts all make bolt ons.