If you want to take the bikes on the train downtown, look seriously at folding bikes. They range in price from a couple of hundred up to several thousand dollars. They also range in design from upright cushy comfort, to lean-and-mean racer. Some are toys, and some are high-end technologic marvels. Most of them have a quickfold option where in 30 seconds you can bag them and board a train. Some can be disassembled and packed into a 30" suitcase that can be checked on an airline.
I got a fairly expensive custom Bike Friday because I'm well over 200 lbs and would be at or above the weight limit for some of the cheaper ones, but if you're under 200 lbs you have a lot more options. Dahon, Swift (available from the original designer, or a modified version licensed by Xootr), Brompton and Bike Friday are a few of the well known ones. Other people may recommend other brands. Check out the Folding Bike subforum if you think this might be of interest.