Generally, you have to use the same brand TX and RX.

BUT....there are now $10-15 "clone/compatible" Rxes for Spektrum DSM2 and $30 Futaba FASST "clone/compatible" RXes. Hobbyking sells them under the "Orange" brand, and other online stores sell them as well. There are also counterfeit Spektrum RXes (exact same look as a genuine Spektrum, but the font is a little "wrong", and the quality isn't as good), which can be hard to tell from the real deal (price is usually too good to be true).

D.