I'd just watch the boards to see if anyone wants to sell a used one, or check eBay.
I got lucky and got a brand new one off of eBay for $350 shipped, regular $550 (It's extended for my GTS).
The guy got a new exhaust from the dealership since the last one melted his bumper off, but his car was already sold (he put the stock exhaust back on) so he decided to sell it on eBay. Gotta do your research if buying off of eBay though, and stay away from some companies that operate exclusively off of eBay, and tend to just look for the everyday Joes like you and me.
On another note, on New Celica. org, there was a group buy going on for pretty cheap, but I don't know if it is still on or not. Might want to look there also.
Regardless, good luck though!