It sounds like they didn't steal a car, they purchased all three of them, from private sellers, for a total of about $20,000. Someone posted this interview with US Marshall on CNN in interview with Anderson Cooper, above. Seems that the Ford-150 was purchased for about $6,000 from someone who was selling it privately. I guess you could go to Craigslist in your community and pick out a vehicle for sale, or something like that. Maybe just sitting at the shopping center parking lot with a For Sale sign in the window, and you call them up and make a purchase.
The US Marshall interviewed on CNN by Anderson Cooper (interview posted above this morning), said that he was surprised also that they seemed to have a well-planned escape plan, but no destination.