I'll second what Steve says. Ask around at local places for their scrap. Many will just give it to you, especially smaller peices as it's not worth their time to charge for them. Scrapyards, welding shops, factories, farm equipment places, etc.. To name just a few.
My factory lets local artists scrounge through our dumpsters for various metal scraps. They love the pre-cut shapes that they can play with for free.
GB :mrgreen: