are you considering caloric efficiency?

I love this list, but I doubt it's accurate to more than an factor of 2. http://efficiencyiseverything.com/calorie-per-dollar-list/

Bananas are not a cost effective source of calories, have very little protein, and boast a fairly high glycemic index.

basically, bananas are trash at being fruit.

First of all, this is discussion about people eating too many calories from bad food. Bananas probably beat most of the snacks otherwise discussed.

And protein deficiency? A 70kg male needs something like 55g of protein (WHO figures) unless they exercise. You are not going to go below that unless you fill a substantial chunk of your calorie intake by eating pure fat.

I eat a plant based diet and weigh about 67kg. On 2500kcal I get about 95-110g of protein, and that is without trying. Had I been a meat/milk eater, this number would have been higher.

Protein intake is generally a problems if you are either starving or very serious about building LOTS ofta muscle.

Valid. Bananas are however very high in potassium, moderately high in Magnesium and dietary fiber.