I can’t give it in money, but I’m on the low end of the examples people have posted. Here are the typical buys, which vary as desired.
Habits: Closest big grocery store, A) go through produce department first, get some red-or-yellow items, some dark-leafy-green items, some fruit, all this in season as it tastes better, is also cheaper. Some potatoes or equivalent (bag of brown rice, say).
That leads to B), cupboard supplies. Seek whole-grain items normally (bread, even w.wheat spaghetti). Sometimes canned or frozen fruits or vegs, V8 juice, not often, as enjoy the fresh. Biggest size jar of nothing-but-peanuts-and-salt peanut butter; piece of good cheese; canned tuna (bought if out of stock). Mayo, tomato sauce, pickles, baking supplies, spices, misc. as desired. Chocolate.
C) Meat and Dairy, get a whole chicken at $1.29/lb or a pork roast at $2.39, or other fresh animal protein. Lunch meat maybe. Milk, butter, eggs, once in a while bacon. Milk is non-fat but that is a matter of taste, and of course calorie/cholesterol considerations.
This takes two twenty-dollar bills and into a third, more or less, and lasts for most of a week. If shopping while hungry, it’s likely to cost more.
Fortunately I happen to like a lot of healthy stuff. Some of this liking is due to slowly changing my habits toward health over time; I am quite self-indulgent by nature.
I’m not forcing myself to follow masochistic rules; I find what I like and cook it for satisfaction.
Strategy: set the oven at 350 F, set chicken in on its back with nothing inside; add a sweet-potato and/or small red potatoes and/or other bakable items. When done I have supplies for a number of microwave meals that can be trimmed according to whim.
Typical day: Breakfast, dry cereal and milk, chocolate milk, tea; lunch, melted-cheese-and-tomato-and-trimmings sandwich with some fruit or tidbit(s); dinner, piece of chicken, slab of yam with butter, green salad or broccoli (mix lemon & mayo to make it good), some small indulgence to end with. That’s a typical example; actual days vary a lot. Treats according to whim modified with some sense.
I don’t buy sodas, beer, or liquor except for hospitality supplies, and that should be from the lifestyle budget rather than food budget anyway. You don’t see me buying a lot of all-made-up-for-you items, but still I only cook about twice a week, while getting a lot of hot tasty meals.