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 :)
When I was in college I managed to get by for 3 months on just egg fried rice and it cost me about £2-£3 a week (about $3-$4). I was only getting 1000 calories a day but I was getting the rest of the nutrients I needed from the eggs and a bag of frozen mixed veg.