I checked out a place near me yesterday, and they had the 1200x600x100 high density (I'm assuming it was hobby grade as he said that's what it's used for) and it was $90, so clark rubber looks alright.. I think I would be happier to just pay for a nice new sheet of the right stuff rather than scouting around for constuction sites and what not, and $45 is pretty cheap.. Thanks heaps 'dangles' for doing that.
Cam