This is the internet in a nutshell; one site provides a very precise answer that’s spectacularly wrong. Another site provides a fantastic wealth of answers, all of which are sort of wrong in various different ways. But if you’re smart enough to reformulate your search as “usda milk price retail,” as I eventually did, you’ll get this extremely authoritative-looking document from the USDA that provides average retail whole milk prices in 30 different U.S. cities for January 2012. The average is $3.69 per gallon. Other reports are available for reduced fat milk, organic whole milk, and organic reduced fat milk.
Moral of the story: the internet makes dumb people dumber and smart people smarter. If you don’t know how to use it, or don’t have the background to ask the right questions, you’ll end up with a head full of nonsense. But if you do know how to use it, it’s an endless wealth of information. Just as globalization and de-unionization have been major drivers of the growth of income inequality over the past few decades, the internet is now a major driver of the growth of cognitive inequality.