there are foam pool tiles @ clark rubber, if you want cheap.. as far as I can tell its the same stuff as production boards 'EVA' .. There are a few different densities I bought the hard, but medium would be better.. they are pretty thick so a bit of imagination is needed to get them to the right shape..(edit* by this stage you will probably have zero imagination and zero patience so they might look less than spectacular)
here are my last ones,
$10 for a tile that you can cut at least 4 padz out of, and they sell contact adhesive at clark aswell..