I'm in the process of shopping for one myself. One time I got stuck in SF when my Appt was delay. I cannot get back on bart transit with my full size bike. Even if I did, I had to get off at the 19th station in Oakland and both has restriction during commute hours. So I ended up waiting it out eating at a place where I can see my bike in view. So now everytime I travel to SF, I end up driving until I get a folder.

There are couple of nice 20" one at my LBS but they run $1200. I saw some at Craiglist for $600 and probably cheaper in your area. Not sure if I need it with a motor for the hills since the motor and battery makes the bike weighing in at 50lbs. However it will be nice to have that feature in case I do have to climb the major hills which so far I avoided.