Cheapest I could come up with:
1/4 onion +
1 can of kidney beans +
3 cups of cooked rice +
1/2 tomato
1/2 lime
Salt, Pepper, Paprica for taste.
1/2 pint of non-fat yoghurt (18oz / 450g)
1 fist full of mixed nuts.
1 apple
1 orange
1 banana
That should cover protein, calcium, vitamin and carb needs for a fairly good diet.