CAI wont do too much if you want raw sound..
It will give you 10-15hp with a tune.
1) If you want sound, then either go the cheap route and delete the resonators from the nismo exhaust.
2) You can add these and gain 8-10hp and some sound.
Megan Racing MR-SSDP-N7Z Test Pipes - 370Z - Nissan performance parts
3) You can get HFC's for less HP gains and less sound. For double the price..
Those are my simple cheap suggestions