Block is ugly, cheap & simple and plenty strong in compression for a quick&dirty solution. Can just stack & glue together with Elmer's if you're feeling lazy.
Pretty-enough is easy-enough if you've got a hint of DIY or wet-glue, paper, crayons and kids.
Sometimes tough to get top even, though. Think about laying 2x4s lengthwise and topping with usual styrofoam to take up the bumps.
Hope this helps.
A