Flavor does not matter, presentation does not matter but the food shouldn’t make you sick, and should ideally have enough calories per day for the average person to survive (2000 kcal min).
Edit: I am not in any danger of starving or malnutrition, nor am I insolvent. I’m mainly asking this question out of curiosity on how people would approach a solution :)
Short answer: potatoes.
Famously, you can survive on a diet of only potatoes. Starch gives you the caloric energy. Skins give you nutrients. Potatoes can be bought in large amounts for not much money in many places.