There are a lot of inexpensive options to choose from

A lot of the Hobbyking/Turnigy Radios are cheap and should work good enough to bash around
http://www.hobbyking.com/hobbyking/s...nsmitters.html

A name brand radio that falls within your $100 would be the Sanwa, it has a waterproof receiver too so your uncle can crawl through deep water as well
http://www.hobbyking.com/hobbyking/s..._receiver.html