I think that our team has a fairly generous budget. We could easily buy all of the materials and components that it would take to make a second robot without getting a complaint from our generous sponsor. (thanks Delphi)
So why did we choose to make only one robot this year? Because of the human resource cost. If you are a team that manufactures the majority of the robot, be very careful that you do not bite off more than you can chew and end up with less robot to compete with because you tried to make 2 robots.
Also, unless you are a rookie team, a lot of benefit can be had by your drivers practicing with a previous years robot.