I spend a lot of time planning fantasy budget shops. I think it's that it gives me a feeling of control and self-sufficiency.
So- this is what I worked out is approx the cheapest way someone could arguably meet all their nutritional requirements :
750 ml skimmed milk
2 oranges
98g onion
Wholemeal Bread 2ish slices
118g spinach
Lentils 82g (dry)
Carrot 98g
White rice 65g
Sardines 3 88g tins a week
Salted peanuts average 78g a day- less on days you have sardines, more when you don’t. (These are cheaper than unsalted and there's not much other salt in their diet.)
The exactness of the ingredients is based on for instance having 2kg rice for the month etc.
This is about 1773 cals, other people could alter it for them if they wanted. I maybe need about 1700, I'm on the smaller side of medium and fairly sedentary.
Obviously I think I'd still have a multi-vitamin/mineral supplement if I were eating this, and you'd need some seasonings etc to make it more bearable. 
So, what sort of things might you make with some of these ingredients (w cheap seasonings etc?) I see a lot of curry, sardines on toast, lentils on toast (?) , maybe some sort of stew, nasty rice pudding w long grain rice and sweeteners... any other suggestions? I don't like soup. 