[GreyingJay]

Depending on what exactly you want to do, you could definitely power it all using a 12 volt wall wart (use the highest current output you can find) or a 12 volt bench power supply (5-10A or more).

If you don't need real motors and motor controllers, you can plug in servos to stand in for motors. Continuous rotation servos would give you a good visual indicator of movement. If you're not using motors or other high current draw devices, you can probably dispense with the PDP entirely.

How many RoboRios do most teams have? If we had the resources I'd want at least three: one set up in a testbed configuration like this, another one mounted in a full drive platform (either purpose built, or reusing a robot from previous years) for autonomous testing, and then the competition robot.