Unless I really have to, I never buy any materials. The last piece was 6" square Ali x 1ft long, and I got it for £20, bought because it was such a bargain, off an occasional advertiser on a web site I frequent. A bit scarred in places, but that soon machines off.
The best place is to ask neighbours, family and friends to have a look though their garages and sheds, or even their gardens, for any metal (and maybe other materials) they don't want, even large nails and big bolts are good enough for some jobs, plus become a scrap yard yourself, it really pays. Ask the people above that before throwing out anything that might be of use, tell them to drop it off. You can then strip it down, get the materials out of it and then when you have enough junk that can't be used, take it down the local tip.
At my last askings, I was given 3" diam x 2ft long of brass and the same in PB, 2x6" diam x 1.5" thick brass bar. Next week a friend is bringing me some steel bar, cold rolled and it is usually 3" x 1" x around 20ft long (in smaller pieces), he works fitting garage doors, and those operating bars are usually thrown away. I cut it up into 6" pieces and distribute it around to whoever needs some.
Over the years, you won't hardly ever have to buy any materials, you just search through your stockpile until you find what you need.
The only problem is finding storage for it all, I have four large garden storage boxes (used for bicycles and lawn mowers) and my workshop full of my ill gotten scrounging.
Help someone out now, and you will be rewarded in full in the future.
John
Just as an aside, if anyone lives nearby and you need some raw materials, get in touch.
