The Washington Post hits on how much it costs to be poor -- the way that the poor are forced to pay more, not less, for virtually everything; if not in money, then in time.
A friend of mine put it most simply. Poor people spend time to save money. Well off people spend money to save time. That's how you know where you are, assuming you aren't living beyond your means.
The WP article isn't bad, but it doesn't really get the full flavor of poverty. When you look poor, and if you're poor long enough you will, you just get treated worse by virtually everyone. They know you don't have money, know you don't have power, and thus know they can push you around, disrespect you or just ignore you.
My favorite story along this line is when I was barely making ends meet by doing odd jobs helping people move, doing yard work and painting houses. One day after painting a garage, I walk into a bank with the check from the day's work (this is in the eighties). I'm disheveled, covered in dried paint, and look awful. The teller wants to hold the check for two weeks. I can't wait that long, I need the money for rent. I walk out of the bank.
I go back to the rooming house I'm living in. I shower, shave and comb my hair. Then I go find my last set of good clothes -- gray flannels, dress shirt, blazer, tie. I put them all on, and I head back down to the bank.
Unlike a lot of people who are poor, I haven't always been poor. I went to one of the most elite private schools in Canada (ranked second at the time, after Upper Canada College).
I wait in line, and irony of ironies, I get the same teller.
She cashes the check.
But I don't say anything, because I know she could capriciously change her mind. I just walk out.
A couple years later, during the same extended period of poverty, I get to the point where I can't even pretend to be middle or upper class. And on occasion I get rousted because, while I'm clean, I look pasty, my clothes are threadbare and my glasses are literally taped up. One time a security guard throws me off the property of a hotel I went into to use a pay phone. In another case, I get tossed off the University of Ottawa campus: I'm beyond the point where I can fake being a student, even though I'm the right age, and was one just a few years before.
In the last ten years, since I ascended back into the middle class, I've never had any such situation come up.
The worst thing about being poor is the way you are treated. There is no rule more iron, in my experience, that the less you get paid, for example, the worse you will be treated at work. Clerks in stores treat you worse. Government bureaucrats can often barely conceal their contempt. And so on.
The upside, I suppose, is that people show you who they are. The rare person who treats you exactly the same as they do everyone else is revealed as the shining gem they are. In particular the friends who stick by you even when you're down and out show themselves to be real friends, as opposed to those who follow the rule given in so many self-help books to cut off less successful friends, and thus reveal their complete moral bankruptcy to the world.
You learn who you can actually trust, who actually cares about you, and who is actually a decent human being who doesn't enjoy being able to kick down on someone they figure can't kick back.
It changes how you see people. Oddly, before I was poor I thought practically everyone was scum (I was a cynical teenager). Being poor convinced me that there were some truly good people in the world -- people who would help you, be kind to you, or just treat you respectfully, even when there was nothing in it for them.
In ugliness and deprivation, beauty and kindness are much much more obvious. All the more so, because so few meet this test and pass.