Affordable M.A. Bag Material?

I'm making myself a big 6' tall and 1' wide punching/kicking bag and I was considering my inner material options for it. First off, I thought of peat moss or mulch, but that won't work. Sand, dry concrete, gravel mix, I don't think any of that would work.

My plan was to have a 6" wide inner tube (made of thick jean material) in the middle of it that would be a very hard material, and then the space surrounding it would be a somewhat lighter material.

Any ideas? Most punching bags are made of a stuffing/bits and pieces of cloth and other such stuff but I can't find anywhere to buy it.

Just found a bunch of threads on SherDog, and what I may do is fill the inner tube with sand and the outside part with shredded cloth... it would take a while, but I know where to get clothes for extremely low prices. Hmmm

I really like how rice feels. It would be way too heavy and expensive to make a 6 foot bag, but I have 120 lbs of rice in one of my old seabags and it is perfect to me. I don't hit it super hard because I don't want to bust the seams, but it is just as good as it was a year ago when I made it.