With a Brompton, you could ride to the train and then ride the rest of the way to work. Why bother with the bus when you can ride? Unless you judge the traffic to be dangerous.

As makeinu suggests, you aren't going to get much exercise with your commute. But you could work your way up to 15 miles on occasion, which should be fine on a Brommie.

If you just wanted to cover the first two miles, you could get an old bike if your neck of the woods is especially safe. Around where I am, trasher bikes get stomped, stolen, or otherwise dismantled no matter how cheap they are.