I wish I could sell my car for $45k when I hit the 50k miles mark hah. My M3 is a commuter too. $46-47k sounds about right. I think people usually compare your price with autotrader's prices.
11 335is, KW1, M3 bits and what not
08 M3 Sedan 6mt, loaded, modded to the bone
Old: 04 M3 SMG