You have to be rich to be poor.

That's what some people who have never lived below the poverty line don't understand.

Put it another way: The poorer you are, the more things cost. More in money, time, hassle, exhaustion, menace. This is a fact of life that reality television and magazines don't often explain.

So we'll explain it here. Consider this a primer on the economics of poverty.

"The poor pay more for a gallon of milk; they pay more on a capital basis for inferior housing," says Rep. Earl Blumenauer (D-Ore.). "The poor and 100 million who are struggling for the middle class actually end up paying more for transportation, for housing, for health care, for mortgages. They get steered to subprime lending. . . . The poor pay more for things middle-class America takes for granted."

Poverty 101: We'll start with the basics.

Like food: You don't have a car to get to a supermarket, much less to Costco or Trader Joe's, where the middle class goes to save money. You don't have three hours to take the bus. So you buy groceries at the corner store, where a gallon of milk costs an extra dollar.

A loaf of bread there costs you $2.99 for white. For wheat, it's $3.79. The clerk behind the counter tells you the gallon of leaking milk in the bottom of the back cooler is $4.99. She holds up four fingers to clarify. The milk is beneath the shelf that holds beef bologna for $3.79. A pound of butter sells for $4.49. In the back of the store are fruits and vegetables. The green peppers are shriveled, the bananas are more brown than yellow, the oranges are picked over.

(At a Safeway on Bradley Boulevard in Bethesda, the wheat bread costs $1.19, and white bread is on sale for $1. A gallon of milk costs $3.49 -- $2.99 if you buy two gallons. A pound of butter is $2.49. Beef bologna is on sale, two packages for $5.)

Prices in urban corner stores are almost always higher, economists say. And sometimes, prices in supermarkets in poorer neighborhoods are higher. Many of these stores charge more because the cost of doing business in some neighborhoods is higher. "First, they are probably paying more on goods because they don't get the low wholesale price that bigger stores get," says Bradley R. Schiller, a professor emeritus at American University and the author of "The Economics of Poverty and Discrimination."

"The real estate is higher. The fact that volume is low means fewer sales per worker. They make fewer dollars of revenue per square foot of space. They don't end up making more money. Every corner grocery store wishes they had profits their customers think they have."

According to the Census Bureau, more than 37 million people in the country live below the poverty line. The poor know these facts of life. These facts become their lives.