Jan. 15, 2012 -- It was six in the evening, and Christine Morris was doing what she loved best: playing the flute.

"I dreamed about being a singer, playing in an orchestra, going to school, getting my degree," said Morris, who is 24 and lives in New York City, in an interview with ABC News' Elizabeth Vargas.

That lifelong passion earned her a spot at a prestigious school of music. But as she inched closer to graduation, reality set in.

"I had just taken out too many student loans … I couldn't take out any more," she said.

Morris' tuition was $10,000 per semester, she said. At one point she had three jobs, leaving no time left for school, she added.

Just one semester shy of her bachelor's degree, Christine left school. But so far waiting tables wasn't allowing her to save up and finish her degree.

So Morris was trying something different. She was having dinner with a man she met on a website called SeekingArrangement.com.

It is one of several "sugar daddy" sites, where men can hook up with potential "sugar babies," younger women who want to be supported financially in exchange for their companionship.

And she's not alone. The site says its fastest-growing population of sugar babies is college students. Some speculate it's a direct result of skyrocketing tuition costs and student debt.

In fact, SeekingArrangement now targets college sugar babies, offering free membership, which in turn attracts sugar daddies, who pay as much as $2,500 for membership.

Who are these men? Morris said some are Wall Streeters, lawyers and businessmen.

How old are they? "Most of them have been in their forties," Morris said.

"For a few decades," Vargas added, laughing.

"Yes, exactly," Morris answered.

Melanie Berliet, a freelance writer based in New York City, knows firsthand what Christine was talking about. She went undercover to write an expose about SeekingArrangement for Vanity Fair.

"It's remarkably similar to dating in the real world," she said, "but the distinguishing characteristic of a sugar baby/sugar daddy relationship is that you openly discuss the financial component of the relationship."

One man Berliet met said in his profile that he was willing to spend $10,000 to $20,000 per month to date and support a companion. To college graduates, who shoulder an average of $25,000 of debt, that's attractive.

SeekingArrangement gave "20/20" a list of colleges it said have the highest number of sugar babies. NYU was No. 1, and Harvard made the top 10.

Some of the men were looking for "arm candy" to accompany them to formal events, similar to a trophy wife, Berliet said.

Richard, a Las Vegas sugar daddy in his fifties who declined to give his last name, said these arrangements were a win-win.

"To help somebody and give them a better life and in turn, they give you a whole bunch of fun and companionship you might not achieve otherwise, that's a good return," he said.

But "companionship" means different things to different people. The term is not necessarily a euphemism for a sexual relationship; some sugar babies, though, say sex is part of the deal.

Berliet said most men she met during her two months as an undercover sugar baby expected "some sexual relationship."

"But this certainly isn't like prostitution," she said. "It was more akin to renting a girlfriend."

In her profile Berliet said she was seeking a "mutually beneficial relationship," the phrase of choice in the sugar daddy/baby world.

What does it mean?

'Sex Isn't a Given; It Is Earned,' New York Sugar Baby Says

"Basically, trading companionship for money," Berliet said. "A lot of these guys will just pay for pretty girls to have dinner with them."

Christine Morris said some of the men she met expected sex. She said she made it known that wasn't her expectation, but also that sex wasn't out of the question.

Pixie, a 23-year-old sugar baby in New York City, said sex wasn't a given, and it wasn't tied to the money.

"They'll bring an envelope and just put it in your purse while you're not looking, or sometimes they'll just say, 'Honey, do you need anything besides the allowance?'" she said.

She said she told them $8,000 or $9,000 per month, which will help with her plans to go to law school. "For some men that's not a lot of money," she said. "Plus, a wife costs a lot more."

Morris said she hadn't made anything close to that yet. She said she received an average of $100 to $500 per date.

David Montrose, 44, is a New York City-based sugar daddy. Montrose, who works in finance, has written about being a sugar daddy on his blog, Sugar Daddy Diary, and in a book of the same title, published in 2011.

Based on his experience, he developed certain rules, he said.

"Think about it hard, and be honest and upfront as you discuss the details" of the arrangement, he said. When a potential sugar baby asks for a certain amount, he asks himself, "Can I afford this?" he said.

Another rule is not to forget it's "no strings attached," he said. "One of the common traps sugar daddies and babies fall into is falling in love with the other."

He said in his experience sugar babies varied widely, from a graduate student in chemistry at a top upstate-New York university, to an airline employee, to a divorcee, older than he was, with two children.

Regardless, he described most sugar babies as "girl-next-door types who need financial help at that time of their lives."

Watch the full story on the full episode of "20/20."