[KenWittlief]

there are two groups of RC hobbie controllers, ones specified for model aircraft, and another for RC ground/water vehicles.

so that is the first thing to check - dont use an aircraft 'band' or frequency if there is any chance someone will be flying model aircraft anywheres near your use of the EDU kit - you could cause their aircraft to crash and burn.

Other than that, AM is the least expensive form of hobbie RC - you can get 4 channel systems for less than $100 if you dont get the servos and nicad batteries. Since these transmitter are 1 Watt RF output, and you will only be operating your EDU bot several feet away from the transmitter, AM will be acceptable for every possible appication I can think of (by contrast, RC hobbiest often fly model aircraft a mile away or more - they are the ones who really NEED FM or other more secure and reliable links).

also look for used systems - I have purchased used ones in the past for $50.

It will be interesting to see how many teams pull these hobbie transmitters apart and rewire them to full sized joysticks and control boxes.