The Syma S107 is a $20 helicopter that is very stable and well documented.  The controller is a 3 channel IR system. 
Here is the helicopter:  http://www.amazon.com/Syma-S107-S107G-Helicopter-Colors/dp/8499000606/ref=sr_1_1?ie=UTF8&qid=1370359260&sr=8-1&keywords=syma+s107
Here is the schematic:  http://www.rcgroups.com/forums/showpost.php?p=17761695&postcount=7820

It would be cool to pull the electronics and replace it with a TinyDuino and shield to make it autonomous.  It would take advantage of the size, weight and lower power consumption of the TinyDuino without a complex mechanical design.