I don't know how well the $300 Chinese eBay intercoolers work, but it's probably another option to consider.
Or just avoid running the more aggressive maps. I think I get plenty of DD power from map 1, which should be safe to run with a car that's otherwise stock.
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