Under $2 each at WalMart, they are actually drawer organizers for silverware or pens and pencils, etc. 12"x3"x2". I've used them a hundred times and although they are cracked, they still hold soap. I let the soap sit overnight, then run a knife around the edges to loosen it before dumping it out.
Then I use a WAVY CUTTER to cut it into bars. Click the link there to see one exactly like mine. I only paid $3 for mine though, so I am sure you find a better price than that one. Sorry, can't remember where I got mine!!