Bayview Metals

They have a $50 or $100 minimum.
As long as you can meet that, you will be treated as kindly as you could possibly expect a huge metal yard to treat you.
They have all metals at almost all gauges and specifications.
They take down your order and the men in back will employ their well maintained and modern saws and tools to fabricate EXACTLY what you want.
As a metal supply shop, they typically deal with welders and professionals who know what they need to know.
BUT they will indeed take the time to explain different grades and different treated metals and alloys, allowing you a more informed option set.
They have handy size and price charts to make phone ordering very easy.
Also they aren't sticklers on terminology, if you know what you want and can describe it - they won't treat you like a dummy because you didn't know the term "cold rolled" or whatever.