Cheapest would be newspaper….then paper towels. Best IMO, is a rough surface tile…and fairly inexpensive, at a cost of about $2.50 to $6.50 per tile, at HomeDepot.
Anyone else have input?
I use a combination of tiles and a mat I made for the bottom. I used fleece and cotton to sew a mat that covers the bottom of the enclosure. I put the under the logs on the basking side and another on the cool side which I place their food dishes on.
I use tiles that are rough surfaced that I got from home depot for 68 cents apiece, and took 18 per tank I think it was. I use cheap washcloths < 18 for 4.00 from walmart> for under food bowls and repti carpet in their hides. You want to avoid any loose particulate substrates like soil, sand, walnut shell and the like as they can be ingested and cause health problems not only in the way of impaction due to them licking their environment but can be dusty and an eye irritant.