I recently tackled the homelink mirror installation to upgrade from the standard mirror with no options. I bought one on ebay for $80 and gave it a shot. The DIY is linked below, hopefully it makes it look pretty easy and some others will give it a shot.
In case anyone was wondering, any mirror with homelink from 2001-now as far as I know will work. Mine came from a 2004 540i, so don't be afraid of what's out there on ebay as long as it isn't broken.