I've done a bit of research, and ended up heading down the route of a KRMx02 in either the 4'x4' or 4'x8' version. We have some applications like building display cases for the school where not having to step the material through the router would be nice. Regardless, it's a nice and stiff machine capable of doing aluminum (shallow passes) with acceptable tolerances for FRC. Price tag is ~$4K-$7K for everything depending on size and sourcing of material.
An other option would be to just purchase something in the size you're looking for. I've heard good things about the
Probotix and there are at least a few FRC teams running them (2468 is one I believe). Just weigh between the challenge of building one yourself, what an acceptable final product will be in terms of accuracy, and how much you will really save. Do you want the router to be a project or a tool for other projects?
Regardless, I think its a great step in to CNC with great value ($$/benefit to a team), and I think it will end up being a work-horse for us... which is why its up next on our upgrade path.
Edit: Adding link to older
thread.