Hey,
Similar thing happened to me, just a tad more extreme
. A bunch of aboriginals were walking into my direction when I was entering a service station and one of them fly-kicked my driver side mirror off.
Because the colour of their skin grants them full immunity with the law I decided to not bother pursuing it.
I assume the actual 'coloured' bit of your mirror is still in tact and in one piece? ie. the only painted bit on the actual mirror. In my case only the part of the mirror that allows for it to fold in was broken.
What I did was go to a wrecker and they got me a complete mirror from a Forrester(i think it was a forrester) that came out around the same time as my car (MY06 WRX) which I scored for about $250. Then the panel on the mirror that has the body colour on it pops out so you can replace it if that bit with your existing mirror's colour if you don't get a colour match.
To replace the mirror you basically have to take off the door, undo a couple of screws + pull out the electronic mirror wires and you're set. I assume taking it to someone else to do might set you back a fortune and its not worth ruining your insurance no claim bonuses for it.
Have a bit of a search for some wreckers that may have something you're after, unless you just want to go for a new part. Because I felt violated by having my side mirror knocked of I didn't want to wait for someone to order one in for me etc etc especially because it happened the night before the Christmas break for me.