If you want cheaper coco-coir, go to a hydroponics store. They sell Pre-expanded ones in huge bags for around $20.00
...as long as you dont mind dealing with their half-baked associates trying to ring you up with their bloodshot eyes
At least lowes marks them down. At Home Deopt, they just throw it away. Sometimes, we throw away perfectly good plants just because the vendors need the room for their new shipment. Its such a waste.
back when I had russian torts, every time I soaked them, I would scrub them with a soft toothbrush just to get the caked dirt off. (they were outside torts)
I would buy a few feet (depending on the size of your enclosure) of pond liner at a hardware/garden store. Its very durable and will last you up to 10 years maybe more.
DO NOT use treated wood! Its not safe for you or your torts. The preservative that they use is laced with arsenic. (poison)