Need help reattaching the side mirror

I have to preface this entry with the fact that I know almost nothing about cars, so expect me to use "thing" a lot as a description.

Someone scraped my 2007 Sentra in a parkinglot. There was very little damage, though the side mirror was messed up. The mirror popped off, and the cover partially detached from the car door.
The attachments on both the back of the mirror and where the mirror attaches to the thing inside the cover (the part that rotates when I use the power mirror adjustment, which is also intact).
There's a crack, though, in the part that attaches the adjustment thing to the car door, inside the cover, and the cover won't pop back into place on the car. I can reattach the mirror, but since the cover moves, it causes the mirror to shake and become unstable when I drive.

Please tell me this is a cheap fix.

Can I remove the cover and just glue the bits back together or does it sound like I need a mechanic to overcharge me for this?

id try it yourself, the mirror cover i saw at my dealer was like 300 bucks or something, and that was unpainted and without labor....

That really sucks. I don't know how to remove the cover, at all.

I'm assuming I need to remove the physical mirror and slide the cover off the base? I'm afraid of really messing it up, then having to bring it to the mechanic or a body shop and they'll be like "WTF DID YOU DO!" and mulitply what they'd normally charge by 6.