The only way to avoid swapping frequency modules under $300 for a system is probably going to be 2.4 GHz system.
http://www2.towerhobbies.com/cgi-bin...&I=LXPZT8&P=SM
Swapping transmitter crystals is illegal in the U.S. unless done by a certified shop. Modules can be swapped. 2.4 GHz avoids the issue completely.