The most affordable option would be to make one yourself if you're good or familar with your car and basic mechanics.
There are some advantages to CAI but for starters, you can replace your filter with a high flow cone type (like K & N) and just attatch it to your intake tube ( you'll have to remove the air box to fit it in) and then you'll have a homemade short ram intake that will help performance somewhat.
I found this too and it might be helpful
http://www.6gc.net/forums/index.php?act=ST&f=4&t=4450Its a forum post with pics of a GT with a custom CAI, if you contact him, that might help more too.