Calories per dollar: the just-drink-vegetable-oil diet. I think the olive oil on that website is unrealistically expensive; real life canola or sunflower oil is way cheaper per calorie.

But I wouldn't find that very healthy. Your body can run on empty calories, but it will accumulate inflammation and lose antioxidants.

Thankfully, the site also points out to "Nutrient Per Dollar" - where it shows you where to get vitamins and minerals. Props for that!