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.

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. I've seen quite a few of the Hitec 7 channel units and everyone seems to like them.

The Polk Tracker III costs $140 new
http://store.polkshobby.com/scripts/...3001&conum=002
Synthesized Transmitter, Synthesized Receiver, one Servo
99 model memory
synthesized for all 72 mhz frequencies
Works with positive shift (JR, Aitrtroics) and negative shift (Futaba, Hitec, Hobbico, Tower) receivers. {Hitec does make positive shift receivers also}
8 channels
various mixes

Hitec Eclipse 7 costs $205 new
http://www3.omnimodels.com/cgi-bin/w...I=HRCJ6015&P=0
Transmitter and Spectra module
7 model memory
Spectra module is synthesized for all 72 mhz frequencies
Works with positive and negative shift receivers
7 channels
various mixes