In 1997 I scrounged the ingredients to make a 3-axis rig that could support the mass of a 3 hp router. The XY table cost $100, and the high resolution z-axis ball-screw came out of the "mixed metals" bin of a local scrapper (a most excellent dumpster dive). The resulting mill has a 17" x 23" xy travel, with ~12" of z. With this addition to my studio tools, I am able to explore 3D toolpaths in wood and other softer materials (for example corian, used in counter-tops):
The machine, and a small animation can be found on the Current Projects page, under "Tactile surfaces."