There are two components to the M Perf Suspension:
1. Suspension Kit - struts/bump stops/etc: $1500 or so.
2. Spring Kit - $500 or so.
You need both, as I learned the hard way...
2012 335i Mineral Gray
M Performance Whore: PPK|Exhaust|Brakes|Performance Suspension Struts & Springs|Black Kidney Grilles|CF Spoiler and Mirror Caps|M Sport 400M|BMWF30.com