Better yet, go to your local R/C auction (usually, hobby shops salespeople know such events in the area) and buy an old transmitter there.
Recently (it was the first auction I went to), I bought a nice working Futaba FG-series transmitter for $8. I just had to replacing the battery, everything else works fine!

Buying a transmitter is better than buying a "controller", which is merely a 4-axes joystick. You can use transmitter to both fly a plane and control a sim, while joystick can only be used with a computer simulator.

Just my 2 cents...