To add to this thread: I recently replaced my radio on the Bav 40 with one from Amazon. It was €19 only, is half the depth of the original car radios and has Bluetooth, AUX in, 4x15W Amp out, a remote control, and comes with installation adaptor cables.
It's been a while since I last bought a standard car radio but man, was I surprised how cheap and small they've become :-)