eBay is probably the cheapest place. I'm not sure what the mounting point of that car is like, but on the w201 and w124 it is relatively easy to add an autodimming mirror.
This one sold for 27.00 and you can usually find them for 30 - 50.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1,1&item=8029389287
Check out
www.2phast.com/500e and then the section on Autodimming mirror with homelink. If you're mounting base looks like this:
then you'll probably be able to add the mirror listed above.
Good luck!