When I backed up this AM, the right side mirror hit the side of the garage (see pic) causing some cosmetic damage as well as misalignment of the two parts. The signal still works and I can still rotate the mirror. Is it a big job costing a lot to fix at the dealer?

 

Taking it to the dealer will be expensive. Try going to a body shop for an estimate but give it a good wash and use a bit of polishing compound to see how much of the cosmetic damage is actually paint transfer from the garage.

 

The complete plastic shell, i.e. front and back part, is around $40 from online sellers, OEM part, maybe $55 with shipping. No need to paint. It's straightforward to replace if you're ok at that sort of thing. Move mirror to end of range so you can reach behind it with a flathead screwdriver, pry mirror from mount, now you can access screws that retain mirror housing. You'll need a set of torx screwdrivers.