If you have the ElectriStar RTF; it came with a Futaba 4EXA, which is a basic computer radio with four model memory.
It has end point adjustment on all four channels, some basic mixing, and exponential.

Until you get more than four planes, or need more features or channels, I'd just buy flight packs. You can "build your own" flight packs at places like www.servocity.com to choose the components you want. Hitec, and others, make receivers that are compatible with Futaba transmitters. Virtually all modern servos are compatible with other brand transmitters and receivers.

When you do want a new transmitter, you can buy some as "transmitter only." The Hitec Optic 6 is one example. Servo City, and others, sell the Futaba 9C by itself. They use the rest of the components in their "build your own" flight packs; or sell them seperately.