If I were going to use the cheapest substrate I could get, it would just be coarse sand. No clay or clay tablets or laterite under it. I would put a very thin layer of peat on the bottom of the tank, add some mulm (LFS gave me some, while laughing at me), then add the sand on top. Over the long haul you have fewer problems if you don't have clay or fertilizer tablets being pulled up on top of the substrate every time you pull out a rooted plant or plant a new plant. And, since nearly all plants do fine with just water column fertilizing, why add more problems you don't need?