What kind of woodworking tools do you have? I've seen homemade jigs for bandsaws that are used to cut exact circles. Also, it might sound silly, but concrete is pretty easy to work with and the forms are easily built. With a little practice, one can get a glass smooth finish. My wife and I played with concrete for a while; we are trying to make our own kitchen counters tops. We got to where we could lay 3' x 3' sections with simple forms and basic tools to almost a mirror finish. Concrete can also be colored rather easily to give some rather intersting effects......Colin