The term economics comes from the Ancient Greek οἰκονομία (oikonomia, "management of a household, administration") from οἶκος (oikos, "house") and νόμος (nomos, "custom" or "law"), hence "rules of the house(hold)".
Brigid has a nice post on the cost of real food prepared at home vs. "cheap" fast food.
Subject came up recently, here. I've been making the occasional medium-sized semi-gourmet pizza, and Joy inquired about the cost of ingredients. Hm. Well... for vague guesstimates... crust costs maybe a quarter, probably quite a bit less. Sauce, likewise. Cheese, if it's mostly bulk mozzarella (i.e., high-protein hot-melt glue) with a little good stuff for flavor, something under $1. Toppings, anywhere from a quarter to a buck and a half.
So, homemade pizza, putting no value on one's own labor, runs maybe $1.75 to $3.00 for a medium (serves one ravenous person, or two with moderate appetites), plus the cost of running the oven up to volcano heat, and wear & tear on the oven and the pizza stone.
Compare the price at your local pizza parlor, where you're paying for hired labor (and the associated non-wage overhead), rent on the business premises, depreciation on commercial cooking equipment, licensing, inspections, and presumably some profit for the owner (also the shareholders if it's a corporation, and figure in franchise fees if it's a chain). Oh, and advertising.
This is particularly bad in high-overhead areas like Silicon Valley, but even in areas with more reasonable costs of doing business, fixing your own food is a lot cheaper than buying it prepared... unless you're bad at grocery shopping, or you could be using that food-prep time to earn money.
Hey, if cooking takes time away from your $50/hour job, by all means buy your food in ready-to-eat form and take advantage of the specialization of labor. But if you have more time than money? Learn to shop for ingredients, and to transform ingredients into meals.
It's amazing what you can do with rice, lentils, and some spices and such.
And remember: prior to the Industrial Revolution, the household was the basic unit of production.