Steel sells on the commodity markets (like gas or oil or pork bellies), so the prices fluctuate from day to day. (At least, this is what my supplier tells me.) So if you go to buy the same piece of steel on two different days you're likely to pay different prices. Lowes and Home Depot can't keep track of the daily price changes and they charge very high prices so they don't accidentally sell at a loss.

You might check your phone book for "steel suppliers" instead- and there are suppliers such as onlinemetals.com that *can* be a resource, but shipping costs can be prohibitive. Some scrap yards will let you browse around to find treasures before they're melted down, but that varies from place to place because of insurance liability.