I've seen plans for one somewhere that used four long 3/8" carriage bolts with jam nuts and washers to allow a 3/4" plywood or MDF platform for the saw to be adjusted up and down. Just put clearance holes through the recessed top and put the bolts down through the adjustable shelf with a washer and jam nut to keep the shelf at a constant height. A nut and washer above and below the recessed top gives you the final height adjustment. Clear enough?
We have a winner.
Thats pretty much what I did. I had some big Bolts and washers already and just used them. I have a plan for a CMS I want and when I get it I will make it more permanent