It's an easy install you could do in your driveway in 30mins. They cost anywhere from $300 up. Most have decent results. Tuning your car helps but might void warranty.
Here's a thread comparing some new ones ( not done yet)
http://www.camaro5.com/forums/showthread.php?t=88637
This is the first test that was done.
http://www.camaro5.com/forums/showthread.php?t=48202