Sparkfun sells 434 MHz transmitters for $3.95 [1]; just hook it up to a coin cell or four, and you should be good to go. [1] http://www.sparkfun.com/products/8

Sparkfun sells 434 MHz transmitters for $3.95 [1]; just hook it up to a coin cell or four, and you should be good to go. [1] http://www.sparkfun.com/products/8946 http://www.sparkfun.com/products/8946