Took me about five minutes to find. 8 pop tarts, 1600 calories, $2. 800 calories per dollar:
https://www.target.com/p/pop-tarts-strawberry-milkshake-8ct-...
But poptarts are low protein per dollar and have limited nutrients.
You could eat bread for 0.75$ a day until you get scurvy.
Poptarts are super expensive.