The LBSs don't carry used, Ask them for advice. craigslist ebay garbage police auctions People you know with 18 yr old children might have bikes for a 13 yr old. In general individuals think their bikes are worth too much, or are garbage.
2000 Montague CX, I do not recommend it, but still ride it.
Strida 3, I recommend it for rides < 10mi wo steep hills.
2006 Rowbike 720 Sport, I recommend it as an exercise bike.
1996 Birdy, Recommend.
Wieleder CARiBIKE (folding), decent frame.