I have used the btmate setup from BT Mate — Simple, Low-Cost Android Garage Door Opener and More
. It cost me about 10 dollars to create the bluetooth garage door opener (newegg.com had the headset on sale for $5 after rebate). I never did anything like this before, but it took me about 30 minutes (I imagine if you have done anything like this before it would be only a matter of a couple minutes). My main issue was soldering. I didn't solder anything and just electrical taped everything together to get it to work. Works amazing.