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 :)
Try figuring out cheapest vegetables available year-round, from which you can make a salad. In the US, this probably includes corn. Where I am, it’s potato, carrots, and beets, which coincidentally make a traditional salad. I boil a pot of them once or twice a week, and chop them in large-ish cubes right before a meal, so preparation takes very little time. Of course, I typically add onions, mayonnaise, maybe herbs.
I’m currently spending about twenty bucks a week on food, and that’s only because I’ve been too lazy to prepare the vegetables, making sandwiches instead.