Outside of a metropolitan area, it's easy (I've done it, and had plenty of money to spare). Inside of a metropolitan area it's a lot harder and probably requires roommates or living in the suburbs or finding a particularly cheap area to live.

... and you're willing to forfeit your position in the gene pool by not having any kids.

Yes, where you choose to live will affect your options depending on your income. Has it ever been any different?

This may sound trite, but it's easy if you stay single. When I graduated college (in the middle of the dot com bust), I made $30k at my first programming job. I lived in a cheap ($525/mo) apartment in Houston and drove a used car which was paid off. Not only was I able to live comfortably (see a movie, buy a cd or eat out whenever I felt like it), I was also able to pay off my student loans at an accelerated rate of $500/mo. Subtracting just the student loan payments would have put me at an equivalent salary of $24k.

That being said, I can't imagine raising kids on that wage.

I mostly agree, and I didn't feel particularly poor when I was a grad student making $24k/yr either. That was $24k with health insurance, though, which is probably another $5k value if I'd had to buy similar insurance privately. Also, I didn't have a big-screen TV, dishwasher, washing machine, or dvr, though I did have a cell phone, internet access, and refrigerator.