The problem with using an arduino is that you don't have a controller. Most teams want to be able to easily drive there robot around.
The vex cortex is a very nice system for only $400. You get the cortex controller and the joystick.
http://www.vexrobotics.com/products/.../276-1604.html
To plug a PWM speed controller (Victors/Jaguars) into it you just need a male to male 3 pin header. (The ports on the cortex are female where the ports on the cRIO sidecar are male)
We retro fit our old robots with the cortex to save on buying multiple cRIOs and having to set up multiple driver stations.
To program the cortex you need to buy a copy of EasyC or RobotC (I recommend RobotC). You can get a 30 day free trial each of them. So you can't use Java but for the most part moving from C to Java is a pretty easy switch, most concepts and functions will transfer very easily.