those are borla. the most expensive thing around.
you can get thrush,magnaflow, flowmaster, dynomax...all for under 150 bucks for the pair. just gotta know where to look. tips are cheap too. you can buy a pair of tips for 40 bucks on ebay.
those mufflers dont have very good "reviews" for grand prixs haha. you kinda get what you pay for with the mufflers.
2005 Grand Prix GT - Corsa Sport Catback, Thrasher Shift Kit, Custom Open Cone Intake, Spyder Chrome CCFL Halo Projector Headlights, CG LED Tail Lights, Pioneer DEH-33HD stereo unit, Alpine SPR-60C 2 way 6 1/2's, Kicker KS 6x9's