For $2000 there is alot of things that cAn be done to boost hp, the cheapest I believe being a cold air intake kit. The best advice i got when I bought my beast was to get used to what she could do and how she drives before tuning it. So far it's been incredible, I love the way she feels in d/s on the highway, creepy is not the word for how easily I can accelerate from 140 to 180 without even pushin hard. It's simply the best thing I've driven, and I spent the summer test driving every top luxury car, from Audi to Mercedes, nothing comes close to how the 335i feels or performs. She's worth every penny I spent on her. I used to think of getting an m3 but after learning that a tuned and dyno'ed 335 can get more hp why pay an extra 30 grand?
Look under the track sections as I'm still a newbie and am still new to the track stuff.
Current Car - 2002 325i
Previous - 2007 335i
BMW lover for Life!