If you want a really "cheap" pizza stone, you can try WallyWorld.
Wal-mart up here in Canada just started selling pizza stones about 2 months ago, and they are $9.99,
so maybe at yours, you may get them for $8.99 or a bit less.
My wife picked me one up for the kitchen stove, to replace my very old cracked one, however, I haven't tossed the older
one out, as it still works ( eventhough cracked )
The stones that Wal-mart sells are the round type, about 16" in diameter, and maybe 3/8" thick ( the usual kind you'll find in the kitchen stores in the malls ) ( nothing great, but give very good results if heated for a good 45 mins to 1 hour in the oven before you slide your pizza directly onto it )