I know Scott, labor cost in this instance is irrelvant though, its time, well lack of in this case :/
When I made a prototype standard size mirror cover I ended up head scratching at how to get them to attach to the mirror body etc. For pure ease I just opted for a simple "bond onto OE cover" affair like the Impreza mirror caps that CarbonMods make.
Re: Unfinished prototype cover:
http://i80.photobucket.com/albums/j1...ova/brapy0.jpg
OE internals:
http://i80.photobucket.com/albums/j1...a/102_1593.jpg
As you can see, OE is compliated simple interference fit. Time consumption central!