Does anyone know if you can get satellite radio installed on a 2003 3- series? Does only Sirus work with BMWs? Do I have to get it installed through BMW or can I do it through some place like Circuit City, etc? BMW was going to charge $299 (receiver), $125 Roof Antenna, $75 bracket, and probably $100 for installation....bringing the total to around $600....can this not be done cheaper anywhere else?