The last time I checked, the poverty line in America was an average of about $19,000 a year. Over the past few years I've been well above that line a few times, and well below it a few times. I can tell you that that makes all the difference. The difference between making $20,000/year and $25,000/year is astounding. Its the difference between just getting by, and having plenty of extra money. Right now, I'm hitting just about $21,000/year, thanks to the added money I get from publishing. If I had to rely on my day job for my only means of support I couldn't do it. That's part of the reason I always encourage people to start a small business. Its a great way to supplement your income. And who knows, if your small business does well, you might be able to quite your day job and run yor business full time.
I'd suggest reading the Millionaire Next Door. Its got a lot of information on how to become wealthy on even a small income. The main key is to live below your means (which is hard to do if you make less than $19,000/year). Buy only what you need. Never pay full price. Invest.
The Millionaire Next Door has case studies in it about people making over $600,000/year, and they can't make ends meet because they spend theri money faster than they make it. The trick is to make as much as possible and spend as little as possible. It seems simple, but millions of people can't do it.