I had mine done at CO's for I think $500ish? I found a coupon on the forums from another dealer and they price matched it. I think after tax it was around $550 out the door.
The cars power delivery is much more smooth, as others have noted. I have also had a return in MPG a tick too, about 1-2MPG highway. Seems to be a nice improvement, just wish the price was cheaper.
E92 Space Gray 335i - COBB, BMW Performance Exhaust (stock tips), style 230 rims, LUX H8 AE's