if you had bought a m3 or rather any car in general during jan-march (the height of the financial meltdown) of 2009, the sales price is basically the same as it is today (couldve basically drove it for a yr without depreciating).
depending on your geography, 2008 car is roughly high 40K. i.e. southern ca is a hot market, a 2008 AW/FOX Red 6mt, 17,000miles fully loaded sold for 48K at the manheim auction. this is auction too. only color combo i've see in months.