If your receiver is a short range micro receiver, a super deal is the Hobbico 8 channel unit. It is 49.99 with the crystal. You just order it on the same channel as your existing transmitter
http://www2.towerhobbies.com/cgi-bin...I=LXMFU5**&P=0
You’ll only use channels 1-4 on your trainer. If you ever buy a transmitter with more than 4 channels, and planes that need them, this unit gives you up to 8. It uses Futaba dual conversion crystals so you can change channels in the future if you need to.