That is the problem I am running into. It is not worth it to the owner to part them out and sell me the transmitter and try to sell the collar separately. I have been watching ebay and craigslist all summer and they sell as a set from about $175-225. There is a guy on ebay selling a new condition one now for $200. This is his third time to put it up for sale so maybe he will get a bite.
I have even thought about parting mine out and upgrading. I have 1 worn out, but working, transmitter, 1 broken transmitter, and 3 collars.