My buddy has it on his 99 GT, he picked up the whole kit used for 300 cdn. I think you gain like 20 hp or something. I don't know how it compares to other CAI's.
Don't waste your money on their 4" high velocity tubes, they only give like 1-3hp more than the 3.5" tubes.
I would call Western MotorSports(WMS) and see if they have any used kits.
I've only heard good things about them, but call them up for more specs