Light Expanded Clay Aggregate. Also known as hydroton or umm other names. Basically it's fired clay balls that people sometimes use for their false bottoms. It can be purchased from vendors, chain pet stores, or, hydroponics stores. I think the pet stores are the most expensive.
No but I found a few hydroponics stores in Chattanooga through google. Take a look. I think that's probably the cheapest. However, if you are only buying it to dry out your substrate, there are probably other ways.