The cheapest place to get them is at LH. Bernie sells them for 75.00. Thats really the cheapest. You can possibly find one on ebay but after shipping you are right about there.

They use AMB RC system. The ggod thing with your own transponder they will always have your number so the next time you go there, at registration tell them your name and your Transponder # automatically pops up. Now it is powered by your third channel on your receiver usually its empty, but if its not you have to get a y connector. Don't worry about it draining your Recv. Battery either it draws like .03 amps or something.