performance modifications for an e46?

looking to add an exhaust kit and possibly some other modifications to my '03 330xi, i am in love with how the Dinan exhausts sound, but would like more than a few horsepower added if im going to spend some decent money on modifications.

if you had, say... $2000 to put anything you wanted on a stock e46, what would you do?

also, how much would it cost to buy a complete exhaust kit (cheap - expensive)? where do i buy it from? is it easy enough to install myself (bolt on) or would i need to pay someone to install it for me? how many hours would it take a mechanic?

thanks