http://www.ussautomotive.com/auto/steelvsal/hood.htm
Above is a quick pricing analysis comparison between aluminum and steel. I changed the prices to reflect current pricing $1.43/lb for Aluminum and and $0.56 for 10-20 Steel, non-SAE grade.
Aluminum cost : $42.32
Steel cost: $32.43
Volume: 1,440,000
Tot. Price Aluminum: $60,940,800
Tot. Price Steel: $46,699,200
Added Cost: $14,241,600
Weight Saving: 49%