There are several low cost single board "PCs" that are capable of performing adequately for offboard vision processing in FRC.
Rasberry Pi has been successfully used, BeagleBones as well.
There are a couple more that come to mind that should be considered.
There is a new
Beaglebone Black listed at $45, that looks very promising.
The
PCDuino ($60) has been
tested by 2073 and is capable of providing tracking data at 15-20 fps. We will be using this and performing further evaluations in off season competitions this year.
Our experience is that the combination of (PCDuino + USB webcam + uSD card) can come in at a cost of about $110. I'm certain the price and performance can be matched or bettered by some of the newer offerings already available and those that will be available soon.