The exception? The LDS Cannery sells milk for very cheap! I calculated that it comes to a little less than $1.50 per gallon. Unfortunately, you can't order the milk online: but hopefully there is a location near to where you live! Check out the list of locations here. It would be good to contact the location to see when they are open. And, you don't need to be a member of the LDS church to buy things from the cannery!
They also sell a lot of other bulk food items, including beans and oats. This order form lists what they have available. If you buy certain items, you will need to can them yourself, and will therefore probably need to make an appointment. If you are buying in bulk, you should just be able to drop in any time they are open.
So, now I just need to make the trek up to the LDS cannery and get some powdered milk. Until then, I will just stick with real milk- it's cheaper. Thanks again readers! You're literally saving me :)