Staples has 40, 60, 80 and 100 qt aluminum stock pots for great prices. They do free shipping to their retail stores and apparently they will price-match Amazon.
40qt for $45 ($1.13/qt)
60qt for $50 ($0.83/qt)
80qt for $57 ($0.71/qt)
100qt for $68 ($0.68/qt)
That's hard to beat...