I would not go for a wood CNC router because of problems with swelling, lengths changing and not being able to provide the proper rigidity.
IMHO the best aluminum based cnc router is provided by
www.finelineautomation.com. It is basically a 2x3 router that is in kit form, the # is FLA100
check them out. Nate is the owner and is a great guy to deal with. He can design a custom size also, if you need it.