ORIGINAL: carrellh
I know of two transmitters that are "shift selectable" which means they can control JR and Futaba receivers. There are probably moreb ut these are the ones I know.
Carrellh and I posted at the same time - the Optic6 in my message above is also "Shift Selectable" and I consider that feature one of it's differentiators over other Synthesized brands. In my opinion all 72Mhz synthesized radios should do this.
ORIGINAL: carrellh
The Hitec might be easy to find used, not sure about the Polk. At $140, including a synthesized receiver, the Polk is very inexpensive. I know one person who uses a Polk and he is happy with it.
Just to offer a different opinion
... my flying buddy had a Polk and it was, in my opinion, junk. He often lets me fly his planes and the feel of the Polk transmitter was horrendous. Everything about it screams "chincy", cheap and low quality. He lost several planes on this radio due to poor electronics. At the end of this radio's life, we had a [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXJUP2&P=0]frequency checker[/link] at the field when my buddy has his polk out. He'd turn on the Polk and occupy several channels at once. He'd turn off the radio and the checker's lights would go off. We did this for probably an hour trying to prove that the radio wasn't the problem ... in the end he tossed the Polk (didn't want to get it fixed, even for Free!!). He ended up purchasing the Optic6 and loves it. Sure it has less module memory (Polk has 99), but there is no price for peace of mind.
-MA