I have up on e-bay two Part 15 transmitters for auction. The first is the Ramsey AM-25. This is new, purchased fully assembled and never used (other than a quick test before listing it). It's currently set on AM 1620 Khz. The cheap wall wart that came with it was heavy and generated a lot of hum, so I'm not including it to save on shipping costs. I did test it with a regulated power supply (not included), and that removed the hum. There's lots of info about the AM-25 on this Forum, discussing both its positives and negatives.
I've also listed a Panaxis ACC100 Part 15 certified FM mono transmitter. This is one of a number of these that I purchased used quite a while ago before deciding to go with the Decade MS-100. I sold the rest, but recently found one that I apparently missed. It has an ICOM wall wart, which is higher quality than the original (the original also generated a lot of hum). This is completely frequency agile, and it sounds great (a cut below the Decade, but then, the Decade is much more expensive). It has a built-in wire antenna. You get the maximum listenable range you can achieve with a certified transmitter with it being mono.
If you're interested in either (or both), you can find the listings on e-bay, or contact me directly through this Forum. I don't accept Buy It Now offers on any of my auctions if there are existing bids.