I don't drink milk or use dairy, so I am not the most ideal person to answer this question. That said, I do believe that I have seen decent prices at Trader Joe's and Target. Also, for some reason, I think when Walgreens has a sale, they can have a decent price for milk. Again, I am just going on a hunch as to what I remeber seeing.
There used to be a great place in Kingsbridge, not far from Riverdale, on Exterior St. by Target that was a direct milk manufacturing plant. I do believe that the focus of the retail/factory concept has changed, however, so I would not recommend a trek there unless you happen to be in the area, at Target perhaps, and want to experiment.
I came across a listing of organic milk products that rates them in terms of quality and commitment to organic methodology that was produced by the Cornucopia Institute. It has some good information as to what constitutes a better brand that could perhaps give you a benchmark to find the better price on a better brand of organic, if that's what you seek. I have used it as a reference when I have to purchase milk products for people other than myself, but I buy them so infrequently and not in sufficient volumes so I cannot really compare prices across stores.
Here's a link to the Cornucopia Institute's list: The Cornucopia Institute