Milk costs about $3.50 per gallon in the USA.
Milk prices vary wildly from market to market in the U.S.
Where I live, where cows are rare, it's $2.39/gallon. In greener regions nearby it's closer to $1.89/gallon.
When I lived in Ohio, the hypermarkets always had it for 99¢/gallon as a loss-leader.
I can only assume that $3.50/gallon is normal for... San Francisco, maybe? Or if you're buying organic, free-range, ultra-filtered, sustainable milk.