Here is a great database for statistics on Mineral and Material Commodities in the United States, annually from 1900 and through 2008, for about 90 commodities and minerals including data for supply, demand, exports, imports, nominal prices, real prices, etc.
The chart above shows the real price of aluminum annually back to 1900. Despite the fact that the real price of aluminum had fallen from $14,000 per ton in 1900 by 64% to less than $5,000 per ton in 1937, Alcoa Aluminum was charged with "illegal monopolization" of the aluminum market by the Justice Department in 1938 (see details here "United States vs. Alcoa").