I must admit in this era of rural development, "dumps", once a fantastic source of free materials have gone by the wayside. No longer can you take one load to the dump and bring home two. I feel sorry for folks who just bag the stuff for the trash collector. We happen to live in an area where "transfer sites" are still the vogue and with a kind word to the fellow in charge he will glean the incomings and set "materials" aside for you to pick on your next visit. A song I wrote a few years back, "The Dump Pickers Lament", addresses this problem. There are plenty of sources of free materials out there but you really have to look around.