Many TXs have frequency modules which can be swapped out. These modules contain the crystal and a bunch of other RF components. The modules for my Futaba 9C are about $50 each. I know guys that just open up their module and swap out the crystal, and it works fine. Problem is that this is against FCC regulations and hence frowned upon by the AMA. I decided to just cough up the extra $$ for a second module and not worry about pi$$ing off the FCC or AMA, or worry that my illegally modified TX might have too much out of band noise and crash a plane on a neighboring channel.

Also some TXs that take freq modules have synthesized modules available, these are more like $100, but allowing you to pick any channel you want, at the cost of a little more power and shorter TX battery life...