If cost is a factor, you can do just fine with one of the basic 4-channel 72MHz radios. They work very well for a trainer or simple sport airplane. As an added bonus they don't have a bunch of extra features that may confuse you as a beginner.

Eventually though 2.4GHz is the way to go along with more features & functions once you have advanced past basic 4-channel airplanes. That's a few airplanes into the future of course.

You may also want to see what is popular at your field. That way people, especially an instructor, will be familiar with it.