First, the density of aluminum is 2.7 grams/cubic centimeter. This is important.
One gallon is equivelent to 3.785 liters, and 100 cubic centimerets are in a liter, so there are 3785 cm^3 in a gallon.
There are 454 grams in a pound, this is needed for scrap prices.
So, take 2.7/454 to get pounds, then multiply by 3785 to get total weight in a gallon, which equals 22.5 pounds.
Now, based off of scrapindex.com, beverage aluminum is going for $0.17 / lb. if it's under a truckload. So, take 22.5 times 0.17, and you get a whopping $3.80 / milk jug.
At this rate, you'd be lucky to get a case for a jug, nevermind a keg. Myth busted
