FYI, a good, inexpensive source for double thick MDF is at resturant supply business', they often stock used equipment, more specifically table tops and bases. The tops are generally 1 1/2" or better and laminated, although maybe not a very appealing color or pattern. :) They make great outfeet surfaces, router table tops, etc. The bottoms usually have a sort of MDO paper layer to seal up the surface which might explain why they stay to nice and straight while being exposed to so much liquid. The last one I got already had oak banding around the edges.
David