You would have to call a dealer. Try calling Pacific BMW goto there website www.pacificbmw.com click on parts and call them. Here's there number anyway main: (818) 552-4750. As for how much it is I don't know.
One thing to keep in mind is that if you don't have the rain sensor then you won't be able to power up the compass portion of the mirror (I know this because I checked with BMW and they told me that they tried to install the compass mirror in a car without the rainsensor and the compass didn't power up at all). My 323i unfortunately doesn't have a rain sensor and I really wanted the compass mirror. My other option is to purchase an aftermarket compass mirror.
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