If it's not too bad, you can just use some Loctite plastic epoxy on the housing -- that's what I did on mine recently.
If it's actually smashed, you can get one on eBay Motors for like $35. (Powered but not heated. Heated is like $70) You could also probably find one at a junkyard for cheaper.
Anyone else find their driver mirror loose? the reason I ask is because I want to replace mine as well due to the shaking. Second Focus I have had thats done this...
Mine is heated, and I can fix the platic if need be, I am a composit tech. But if it was cheap, saves time. The mirror it's self, needs to be replace, so I guess I'll check e-bay. Thanks.