2 RER-B (CDG) Tickets on eBay
 

There are two tickets for the RER-B from CDG listed on eBay, starting at $10, ending Nov 15, $1 s/h.

"Transportation from DeGaulle Airport to downtown Paris"

My one question would be...without going home to check...I can't remember if the tickets get cancelled when you put them in the machine (on the back?).

Yeah, they do... as with anything on eBay, you have to go on faith a little, and the seller ratings...

I think they would be good until annual price increases (July?), or would they still be usable even after that?

http://tinyurl.com/2puzfv

It was impossible to find again by searching, so here's the link

If they are single tickets, they are usable even after prices change. Other metro tickets are. The seller should be selling them cheaper, as they only cost about $12 now for real. Why would anyone risk buying bogus tickets from some stranger on the internet only to save a couple dollars.