[misha]

The DIY's aren't that difficult, you just gotta go slow and be patient with it.

Cheap HP: A Cold Air Intake (CAI) is your first step. A name brand system (Ingen, AEM) will cost you $230-300. But other systems (with absolutely NO disadvantages) cost as little as $50-150 and perform just as well. There's even a DIY on this site showing how to build your own for about $30.

There's a lot of love around here for Borla and Mussa. Half the posts on this forum are about "how does this or that exhaust sound?", so there's tons of info in here. If you're quick you may still be able to get in on the Borla Group Buy--a sposored vendor is offering a great discount to a group of ppl who pay in advance--but it ends tomorrow. Follow the links from the main forum page to Marketplace: Official Group Buys.

Exhaust will cost more than your budget of $300-400, but it's the next step after you get an intake.