There are a couple of good options to cutomize the intake for cheapo bucks. I did a Dinan-like Ram Air for my 328i for less than 40 dollars. I even think its a bit more efficient than the Dinan since it doesn't share the same inlet with the brake cooling duct. Check my reply on the following post;
http://www.e90post.com/forums/showthread.php?t=626376