I have a 2009 Mazda3 Hatchback that just made it through hurricane Isaac in nearly one piece. A banana tree fell and knocked off the passenger side mirror, ripping the wires and all. The dealership wants $300 to replace it, so I am hoping to do it myself. Does anyone have instructions or a link that might help?

 

Ha, $300. Absolutely ridiculous.

Replacing the side mirror is super easy. To remove it you open the door, pop loose the triangular panel (where the tweeter is if equipped), unplug the harness plug, remove three bolts and the housing comes loose. Reinstall the new one in reverse order. Start to finish should run you about five minutes of time.

As to the replacement itself..... that's a different matter. The entire standard power housing for the 1st gen runs around $60-70 from the dealer iirc. The heated housing is about $105. I'm not sure if that includes the painted cover or not. Most just come with a plain black cover and expect you to swap the one from your original mirror, though if yours was destroyed by the tree that wouldn't work too well.

You can find complete mirror housings on rockauto for $26 for the non-heated power, and $30 for the heated power. Here's the kicker, the 3 is prewired for heated mirrors all the way up to the plug into the mirror housing. All you need to do for a full replacement is buy the one with the heated glass/wiring and plug it in and you'll have heated side glass keyed to the rear defroster. You can also retrofit heated glass into a standard power housing by running the 12" or so of wiring through the housing yourself. That said just the glass from Mazda runs $45/side, and even from rockauto it's $35....... yup, more than the full housing that's wired already.

If you want to pay more money and get a lot of toys out of the process then thespeedline.com offers a full replacement housing for about $200 which offers:
-power
-power folding (i.e. the housing folds against the car)
-LED puddle lamps
-LED turn signals in the cover
-blue tinted/heated/wide angle glass

I myself retrofitted the heated glass to my car many years ago and love it pretty frequently. I originally put the OEM glass in and later swapped in the blue/heated/wide angle glass from thespeedline (not the full housing, just the glass). Of course at that point you couldn't find the entire heated housing for only $30 otherwise I would have done that. HERE's my walkthrough on my instalation. Hope that helps.