One item I love keeping around the house is powdered milk. I use it mostly when making bread, but sometimes I like to keep a pitcher of it in the fridge as well. Growing up I had a friend whose family always drank powdered milk. I personally don’t care for the taste of it, but I have found other ways to use it that save our budget.
EDIT: This all depends on the brand. This comparison was using Peggy Layton Brand. The brand I currently use, Rainy Day Foods, only makes 5 gallons, but also only costs $13. Do your homework, and check the brands servings per container to get the most for your money.