I've seen used 993 mufflers go up for sale pretty often for reasonable, and see them all time at Porsche swap meets, not to mention, they're stainless. Check out an old listing:
http://forums.pelicanparts.com/showthread.php?threadid=72627
Now, I think the hot set up would be a pair of 993 heat exchangers mated with a pair of stock 993 mufflers - imagine the potential! If the're good enough for a 3.6, then . . . . . . And those come up for sale all the time too. You only need to cut off and rotate the flanges of the right(?) heat exchanger because Porsche decided in their wisdom to do so. But that should be cake, with the new TIG.