The cheapest most versatile breakfast: oatmeal

You can buy rolled oats for pennies on the dollar. Here's how to make a perfect bowl of oatmeal:

Combine 1 to 1 to 1 of rolled oats, water and milk in a saucepan and bring to a low boil, then let simmer on low for 5-10 minutes. Once it's creamy you can add anything you want and have on hand (fruits, nuts, spices, syrup, etc.).

If you want to go cheap on milk, buy a bag of powdered milk. It's super cheap and never goes bad and you always have milk on hand.