The 1M rear retrofit is easier said than done. The problem is that the rear quarter panel is welded on, so it takes a LOT of work to replace it. The only rear-end conversion that I know of was Tony135 (just last week), and he said that he spent over $6,000 just on the rear quarter panel conversion. And that was done by LTMW, which usually has very good prices because their BMW expertise allows them to do the same work in fewer hours.
If I were in your place, I'd get something like this:
Probably cheaper through Schmiedmann.
2008 135i Montego Blue sport pkg, premium pkg, Logic 7 sound, iDrive/Nav
Mods completed: JB4+ & FBO || LSD || BMW-P suspension + F/R sway bars || 18" Breyton GTS-R || M3 front bushings || Vogtland camber plates || BMW-P rotors + Stoptech pads |||| Acquired, not installed: BMS WW Meth kit || Logic HVI intake || Mishimoto OCC |||| Shopping for: Summer tires