I would totally pay myself a visit to Active Autowerke if I were you.
9940 Southwest 168th Street, Miami, FL
They are one of the best in the bimmer mod business and they wont make you feel like a total idiot.
M3 exhaust wont be possible at a reasonable rate. Sorry
But AA just released an exhaust for your model; and its quite on the budget. Around $600 if I remember correctly.
Go pay those guys a visit, but remember to secure your jaw before going there. Or else its gonna drop off big time.