these guys have some pretty fair prices.The Intakes and Exhausts on our site are your best bets. (link below)
Turbo is a pipe dream right now without a large budget and a second car, etc.
intakes and exhausts generally provide marginal gains. i saw a dyno that shows the HKS boosts it a few HP, and it sounds/looks great. the exhaust as well will provide those benefits. i think i saw charts on those systems as well, but by widening the pipes and removing restrictive parts (extra muffler chambers) your bound to increase air flow. very few cars wouldn't benefit from intakes/exhausts.The OP asked for increase HP. I looked at the intake and exhaust on your site, but there is no data on HP gains with those two items.
You can stay stock... no power gain.. no warranty issues $0Lots of money for little gain, but I guess it's up to the individual and what they think is cost effective and worth it.
This what I did for a few years with my S for VERY little actual gainYou can add CAI / Exhaust... small to moderate power gain, better sound maybe.. shouldnt be any warranty issues (Magnuson-Moss Warranty Act) Usually under $500-$1500
This is what I did later to the S and would never go back. I should have just saved my money from the start and went with boost once I could have afforded it. Would have saved A LOT of money in the long run.You can go forced induction.. major power gains... probably will blow your warranty away totally. $3000 up.... ( this is a after warranty expires thing, for me! Probably:sadwavey