Julie,
Look by the bras. They can be kind of hidden sometimes, but they're usually on the same racks. They have two kinds - the silicone ones and the water-filled ones. The water filled ones are FAR cheaper, but the silicone ones will last longer I'm told. I've had some for several months, and they look almost as good now as the day I got them.
And, by the way, in our part of the country, they're $15 or $16.
Carol