Non-dealers can definitely do it for cheaper, but make sure they have the right specs and procedures... I usually go to dealers for alignment just for a peace of mind... because if they mess with you, you can call BMWNA...
2011 E92 M3 DCT
1991 Spec Miata
2008 E92 M3 DCT - KW Competition 2-way / Brembo 365 BBK / OMP ARS racing seats / rear seats delete / GT4 aero / AiM EVO4 data logger / SmartyCam racing camera
2008 E92 M3 6MT
2008 E92 335xi