instead of buying an intake, the cheapest and easiest way to do one is to take the air box off, and get a 3.75" aluminium or whatever, ring shoved into the accordian style intake tubing and then clamp an air filter onto it.

I used a 4" aluminium tube on my last grand prix, but it was a tight fit and was a pain to get in. the tube was 10 bucks from zzp. and they only sell a 4" tube.