I have recently discovered extruded polystyrene insulation boards for my terrain pieces and am having a blast. I'm sure plenty of tabletop gamers have used this stuff. It's cheap ($30 for a 2"-thick 4'x8' sheet), easy to carve, lightweight, and holds up well after a good coat of latex paint. I am currently working on a set of tunnel and brick walls. This base is just cardboard, my next step is using a big piece of 1" board to make a textured base. The best method I have come up with for imprinting a move grid is pressing chicken wire fencing into it. The fencing is perfectly sized, 1" hexes, but a little stretchy. I am open to better suggestions.