I just finished rehabilitating a full sheet machine so it's time for my quarter-sheet workhorse to go.
I have a Grunblau "Platform CNC" built from the second or third batch of kits he sold. See here for more info on this machine:
Platform CNC - Designed by Brian Oltrogge
It's a great machine with a supportive online user community (that you won't find by Googling because it's by-invite ... sigh).
My machine is in great shape and is about as professional-class a quarter-sheet machine as you're going to find.
I've built a 4-zone vacuum holddown system, installed a water-cooled spindle with a closed loop cooling system mounted on the gantry, and equipped it with a KentCNC dust shoe and an easily detachable z-height touch plate. The spindle is driven by a Frenic Mini VFD, and all other electronics are mounted in an enclosure designed by a member of the PlatformCNC community and sold as part of a group buy.
The machine is mounted to a welded steel base that completely encloses the electronics, the vacuum system, and provides storage for various bits and pieces.
The control computer lives in the base and has a "remote on/off" button mounted to a very heavy duty swingarm that holds the keyboard, monitor and mouse, and includes mounts for cutters and collet wrenches. The control system is Mach3, but could readily be changed to Mach4 or another system if you prefer. Stepper drives are by Gecko.
This is a sorted-out, heavy duty machine and will happily work all day every day.
$4950 obo
-Ben