Hmm. Great question. Yes, I do sometimes tally up meals, like last night when I made a pasta dish we both love and I splurged on 1lb of good quality fresh mozzarella to go in it = $13 investment for a huge bowl of food. Anyway, cheapest meal that we all like: rice and black beans with some kind of veggies added. If you buy rice in bulk and cook the beans yourself from scratch AND use cheap veggies like carrots, you're looking at about $1-$2 per large pot full of food. It's not glamorous, but it IS budget-friendly.
Can I share a personal fav hint? Go for green cabbage instead of lettuce. 3 heads of romaine go for around $3, but a smallish cabbage is about half that price. You can cook it lots of ways or shred it for coleslaw or pita fillings.