brings up a good point. Most mail order companies will charge extra (real shipping cost
) on heavy weight items such as substrates. You can usually figure about a dollar a pound in such cases.
The only exception that I'm aware of, is Dr Foster & Smith Petwarehouse. Even when ordering heavy items, ie substartes, normal shipping cost still apply. Even though their price is $19.99, depending on how much you order, it could be cheaper to order from them.