The term "low-income" is usually a synonym for "poor." But I just interviewed three people who wouldn't use that word to describe themselves, even though they live on $18,000 a year or less -- in two of the cases, much less -- without going into debt.

Their ages are 25, 44 and 60. They're all college-educated and have chosen to live frugally so they can pursue their own interests.

Their stories are relevant for a couple of reasons. First, they show what's possible when you let go of consumerism and the hamster wheel of spending too much and then having to work to pay off your debts.

Second, their thrifty habits offer lessons on how you may wind up having to live if you don't get cracking on building up your retirement savings. That figure, $18,000, is about what you'd get over a year if one were to draw average U.S. Social Security benefits (now about $1,200 a month) and tapped 4% of a $100,000 nest egg.

(Four percent is usually considered a "sustainable" withdrawal rate, meaning you're unlikely to run out of money before you die. The $100,000 nest egg at retirement age may be a stretch for some; Employee Benefit Research Institute surveys indicate half of all U.S. workers have less than $25,000 saved (.pdf file).)

Here's who these three frugal folks are:

Tyler Tervooren, 25. Until recently, Tervooren earned $56,000 a year as a construction manager. But he lives so thriftily in Portland, Ore. -- his expenses are about $14,000 a year -- that he was able to save the bulk of his salary. He's now enrolled in a state program that allows people to collect unemployment benefits while they launch their own businesses -- in Tervooren's case, a blog called Advanced Riskology that encourages people to take more risks in their lives.

"Since I earned so much but spent so little, the amount of unemployment insurance I get covers all of my living expenses and actually allows me to still save a little bit," Tervooren explained. "My savings cushion can support me for almost four years -- (even) until I'm 30, if I need it to -- before I have to start earning money again."

Nancy Tudor, 44. Tudor earns about $10,000 a year from two part-time jobs, and she says it's enough to meet her needs. She's earned more in the past -- she recently returned from a job teaching Renaissance history in London that paid about $30,000 a year -- but prefers her simpler life in Albuquerque, N.M.

"I had the apartment overlooking the Thames and the flat-screen TV. It just felt really empty," Tudor said. "I decided to come home to the desert and be a lot simpler."

Carol Holst, 60. Once upon a time, Holst was married to a corporate executive and raising two daughters in Beverly Hills, Calif. When the marriage ended two decades ago, she turned down the court-ordered alimony, figuring she didn't need the money but that he did.

"It would have reduced his lifestyle and wouldn't have changed mine," Holst said. "I'd still be living in a one-bedroom apartment in Glendale, and he'd be cursing me."

Holst said she's figured out how much is "enough" and lives happily on the $18,000 she nets from her part-time job as an office administrator. She enjoys the work but really likes the time it allows for her true passion, which is sharing what she's learned about voluntarily simplicity. From the bedroom of her apartment, Holst runs the website Postconsumers.com, which promotes the idea that you don't have to buy to be happy.

All three credit their parents for helping to instil the ideals of thrift and careful money management. Tudor also remembers grandparents who talked about the Great Depression and a prevailing ethic "that if you wanted something, you saved up for it."

That includes education. Tervooren attended an in-state university with inexpensive tuition for residents, and he worked several jobs to pay for it. Tudor got a master's degree on a scholarship that included student housing and a $1,000-a-month stipend, which was enough to cover her expenses and those of her now-grown daughter.

Tudor asked the girl, who was 6 at the time, to identify what was most important to her, explaining that they didn't have money to buy everything they wanted.

"She wanted money to buy books . . . and to take dance lessons," Tudor remembers. So Tudor carefully budgeted money to cover those expenses. Tudor believes that explaining their financial situation and soliciting her daughter's input staved off demands for more stuff.

"She understood," Tudor says. "It wasn't 'I want, I want, I want' all the time."