It must be a conspiracy by the corn and milk producers to screw the middle class.
Add wheat to that list. Wheat prices have also doubled. So has gold, silver, platinum, copper, steel, palladium, zinc, nickel and all other commodities. It's a huge worldwide conspiracy to screw consumers. Wait a minute - do you think it could have something to do with the US Dollar crashing to all-time lows? Nah, a conspiracy sounds more interesting.
You might be right about the price rigging of other commodities. After all, the dollar is not even 20% lower than this time last year, yet prices are up 100% in the face of bumper crops. So, once again the lower dollar and supply/demand theory falls flat. Let's fix the oil price rigging problem and apply what we find that works to the other commodities you mentioned.