I never thought of getting one but I now realized why my set would move slightly when I beat on it. So today, Musicians Friend has the Road Runner Drum Rug on sale for $69.99. It's still too much just for a rug. Any other suggestions?
You can go to hardware stores or department stores and buy area rugs. You do have to know how big a footprint your kit has to get the right size rug. If you opt for a smaller rug make sure that your throne and bass drum are on the rug, that way the kick wont move away from you.
My kit sits on a rubber backed "rug" that is supposed to go under large area rugs and keep them from moving when placed on hard floors. A drum rug also allows you to mark where everything is supposed to go, so set up at gigs is easier.
That On-Stage one is just a glorified yoga mat. Would work no doubt to prevent slippage and stuff, but eventually looks like it'll wear out or tear if your not careful. I get my drum rugs from Rugs.com - they have [mostly] every conceivable size you could need and pretty good prices.