A Jug of Whey Protein will be cheaper than Chocolate Milk if you compare the price gram-per-gram.
But there are a ton of reasons why Chocolate Milk isn't that great. The fat content will bring down the meal's glycemic index thus slowing the speed of digestion. The vast majority of the protein in Chocolate Milk is Casein protein, which will digest slowly as well. The sugars found in Chocolate Milk are going to be either lactose from the milk or fructose from the corn syrup.
The lactose won't be used very effectively by your body for glycogen storage and the fructose will have to be processed by the liver before entering your blood - thus not only slowing the digestion of those sugars but also making those sugars more likely to become fat than to be stored as glycogen.
You might meet a few dudes at your local Ballys who "Can just fuckin rep out with 225 and make it look so easy!" or "Have finished a triathalon!" who swear by chocolate milk. But no one in America whose really got their shit together and is really kicking ass is drinking chocolate milk post-workout in this day and age.