Which is cheaper, Cow's Milk or Formula?

After G reaches one years old, everyone told us that we can switch to cow's milk instead of formula, once he adjusted to it. Some people also commented that it is much cheaper to use cow's milk then formula. That seems intuitively true. But, don't you want to really know? Let's work the math by calculating the cost per 8 oz bottle of formula/milk:

One can of Similac costs about $20 here. It contains 728 grams of formula powder. You use 8.5 grams per 2 fluid ounce of formula. Therefore one can makes 728 / 8.5 / 4 = 21.4 of 8 oz bottles of formula. At $20 a can, that's 20 / 21.4 = 93 cents per bottle.

One gallon of milk costs about $4. One US Gallon = 128 US fluid ounces. Therefore, one gallon of milk makes 128 / 8 = 16 of 8 oz bottles of milk. Cost is then $4 / 16 = 25 cents per bottle.

So the different in cost is pretty high, 93 cents per bottle vs 25 cents. Not to mention, it's quicker to make a bottle of cow's milk.