If you just mean axlebacks, save the money and do it your self, the S197 mufflers are easy to install with just a couple of hand tools and jack stands.The Borlas fit perfectly !!
If you meant X-pipe & Long Tube headers (full exhaust) :
Gearhead Garage in Gilbert, AZ (gearheadgarageinc.com), he did my LT headers and X-pipe, very pleased and he doesn't charge outrageous amounts for exhaust work, the LT header and X-pipe w/cats install was only $450 (other shops quoted as much as $1000 for the same work)
PSR(Performance Racing Solutions) is another good shop in PHX
Duffee Motorsports is well respected as well, even has prices for common performance mods on his site:
http://www.duffeemotorsports.com/latemodel.htm
Good Luck, hope this helps