Well i only payed about $400 for everything from a salvage yard and I did the work myself, which was a total bitch since I havent done much of this before, but the result was noticeable. Mostly about 4300 RPM when the second flap actuates is when I notice the biggest difference. I still dont have a tune for it and that should help a little bit more. But in the end of the day, I would do it again given that I got a good deal on the parts again. As with installation, I had a friend help me for a bit. That definitely helped. Going in with minimal knowledge of how to change such a thing, it took me a saturday and sunday. About 6 hours saturday and 4-5 sunday. The biggest pain was just disconnecting some of the hoses and things like that. But it saved money so I think it was worth it for me.
http://www.e90post.com/forums/showthread.php?t=727141.
The charts on that graph seem to portrait what I feel driving it.