I use very little salvage metal. I don't have an easy source, or the time to scrounge. I do keep an eye out for deals, and I try to keep enough stock on hand to make just about anything I might want at a moment's notice. My home shop time is precious, and the cost of materials seems trivial by comparison. Maybe that's partlyt because in the guitar shop, I'm using materials that are REALLY expensive, hard to find, and need to be stored for long periods to "season." You know, like rosewood, ebony, ivory, and exotic inlay materials. Because supply can be cut off at any time, I try to keep at least ten years ahead of need on the stuff that's prone to supply problems. (Now, with the CITES and Lacy Act issues, I wonder if ten years is enuf.)
Here are my faves:
Aluminum (6061) - cheap and easy to get
Brass (360) - least expensive, machines well, looks great, etc.
Tool Steel (O-1) - machines more easily than W-1. Great for tool making
Stainless Steel (303) - machines way more easily than its cheaper counterpart, 304.
Steel (1018) - least expensive, good strength, and readily available at local yard. I use mostly cold-rolled.
Leaded Steel (12L14) - it saws, turns, mills, threads like a dream. Rusts like crazy, so you gotta watch its uses, and it's not a strong as other alloys. I use it a LOT. It's what I use to make the shank of my
JACK the GRIPPER tools. I cuts twice as fast as 1018.