best to filll a muay thai or heavy bag?

I had an instructor fill a MT bag with old t-shirts. seemed to work pretty well.
i have heard of all sorts of things to fill it with. Sand, rice, corn, rags. I have an everlast bag an its filled with shredded cloth and is rock solid on the bottom softened up on the top though. The way that seems the best to me though i have never tried it is to fill some heavy duty trash bags with sand making a ball surround that with cloth then put a piece of foam or carpet scrap on top then ball of sand surrounded with cloth and repeat. The foam keeps things in place and keeps it from settling. The problem if you fill with stright sand is a heavy bag would weight like 500 lbs. The sand core gives it a solid core and you wont need to round up 10 tons of rags.
Sorry to bring back an old post but......

Was looking to buy an unfilled heavy bag to save $$$ but the different filling methods still don't make sense to me.

I know alot of filled bags have shredded cloth in the inside but how the fuck do you find enough cloth to make 100+ pounds with?!!!

How well does the sand bag method work cause it sounds like less work than rounding up 100+ pounds of old shirts and rags

I'm on a severe budget or else I'd buy a filled one... or should I just wait a while and buy a prefilled one...basically will the way I fill it (above methods) work as well as buying one prefilled?
Like I have a prefilled everlast and i am about to perform an operation on it. Because there is no layers the bottom is rockhard while the top has gotten quite soft so i am going to try the sandbag core method for the top since i cant fill it with loose sand in case i wanna do floor work i let you know how it works if i get around to it soon i cant see how it wouldnt though
the shipping on a filled bag is what will kill ya.