I very nearly spent over $1500 on a set of Remus Race mufflers for the 335i, this simple modification saved me over $1000 and gave me the exact sound I was looking for. In combination with the BMW PPK tune, the car is absolutely perfect for a fun daily driver. If you can get your hands on the factory Performance Exhaust for cheap, go for that too, it's basically the same thing. I just got tired of scouring junkyards...