i recently picked up 2 identical old folders at a swap meet. both are in non-functional condition but the hope is that one can serve as parts for the other. they were $10 for the both, so it wasn't a big risk
i generally am not a big fan of folders, maybe it's just the aesthetics that i find a little gross, but the MARC train here from baltimore to DC doesn't allow any bikes except folders, and i hate not being able to bring my bike to DC when i visit.
dahon has been making folding bikes for a long time and are quite good, at a cheaper price than brompton