Rouen

As some of you know I've been working on a 1979 schwinn varsity, I'm not sure how much more I really want to put into this bike. So given that my commute is partially done by bus with a maximum of 2 bikes on the rack I've concluded that a foldable bike may be a good investment. so I am open to recommendations on a folding bike for a 5' tall adult in a moist area with a bunch of hills, preferably under $500.

Thanks