You joke, but a friend of mine was planning on using old wheel weights in soft bags. Figured he would have unlimited access to free weight. It gets expensive!
Hmmm. Not a bad idea. A little time with a rake at the shooting range backstop works too.
If you already have all the diplomas you need and are willing to risk the fumes you can find weight molds for sale and melt all that stuff down into weight belt lumps.