You have to pay to play with BMWs.
BTW there really aren't any serious performance mods for the N52 (328i)
Well there are but it's only recommended if you own the car and are out of warranty.
-Three Stage Intake Manifold Swap and a Gintini 330i conversion flash (Huge power gains)
-Search for exhaust
-If you have 6MT BMS Clutch Delay Valve
-lighter wheels/ get rid of run flats
-M-tech aero kit
-BMS Powerbox (Cheap easy gains)
There are a bunch of goodies, but it is expensive!