Here are some pre-cut diy kits for Mini's on Fleabay:
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=380039592113
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=350072572883
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=220236126591
Although, I have seen a few diy tint jobs and none of them looked great. You might just pony up the $150-$200 for a pro job. Or if you want the best stuff in the Valley, Call Danny's In N. Scottsdale. They install the Huper-Optik ceramic stuff that is much better at keeping the heat out. It will run you $350+ though.