It would make sense to sort them by film speed (DX code) and number of frames (mostly 24 vs. 36). Some cameras only accept setting film speed by reading the ISO from the cassette. And some cameras will only expose the number of frames encoded in the DX code.
You could try here on Photrio. It's probably one of the most accessible marketplaces in terms of cost and it gets you into contact with a relevant audience. You need a paid subscribership to post ads, but this doesn't cost all that much. eBay is the other logical alternative.
Can't really say much about an asking price; never thought about it. I have a good supply of these myself, so I never had to look into it...