Kim and Greg Castles were so desperate for a baby, they risked spending 15 years in jail.

How much is having a child worth to you?

Nine months of carrying a growing baby? The better part of a year going to events without alcohol? Perhaps a few thousand dollars in fertility treatment?

What about the risk of almost two decades behind bars?

This is the most tragic predicament facing Australian couples who are so desperate to have a child of their own, they’re resorting to paying for donor eggs. It is, by definition, an illegal activity in Australia, carrying punishments which can include prison for up to 15 years.

Tonight’s 60 Minutes explored the complexities of the IVF black market: a suffocating vortex of vulnerable parents, greedy donors, and and a very human and inherent desire to procreate.

For Kim and Greg Castles, it's a market they know too well. After meeting later in life, the couple were in their 40s when they decided they wanted to start a family together.

In 2007, defying most odds, the duo had a baby girl Stephanie. But when the time came to give Stephanie a little brother or sister, Kim miscarried twins and the couple was told their only option going forward was egg donation.

"My initial reaction was no. I just thought no. I just, if I can’t have my own child, I don’t want someone else’s," Kim told reporter Allison Langdon.

But a mutual yearning on Stephanie's behalf for a sibling, and on Kim's behalf for another child, meant it wasn't long that before the 50-year-old was drafting an ad for the local paper, looking for a "kind and generous female interested in helping to finish a much-needed family."

She soon learned 'kind and generous' came with a price tag. An illegal one.

"'What’s in it for me?' That’s basically what they’d say," she said.

Playing into the bedrock notions of supply and demand, these young female donors could demand whatever price tag they liked.

"It's just the way the world is nowadays. It’s just all money, money, money... you’re hoping people would do it for the goodness of their heart, helping another person," Greg told the program.

For Stephen Page, a leading family law expert, Australia's complicated donor laws are creating a thriving underground trade in human eggs.

"When you have desperate people, there will be others out there, sharks in the water, trying to take advantage of them. We’ve seen it happen with surrogacy; we see it happen, unfortunately, with egg donation," he explained.

For the Castles, it wasn't until Kim was approaching her 51st birthday that they met their match: a 23-year-old egg donor named Jade Morgan. With Jade's egg, Kim gave birth to the couple's now seven-week-old daughter Nellie.

Although Morgan never specifically asked for money in return for her eggs, the Castles decided they would pay for all of her medical expenses and gift her $5000 for some dental work. Objectively this is a small price to pay for a child; but it's a price that could see them charged and sent to prison.

Despite the legalities of the situation, Kim denies the act was unethical.

"She’s done so much more than we’ve done for her. We’ve just paid for her teeth – so what?"

Stephen Page believes it's perhaps time the law was reviewed.

"For some reason these women spend 50 hours, multiple injections, have a shot in the stomach every day, have the risk of too many eggs being pulled out and as a result they may die, and they don’t get paid," he said.

For Kim Castle, there seems to be very little in it for those donors who are giving, and everything on the line for those who are receiving.

"They’re giving so much. They’re not just giving an egg, it’s a family they’re giving. They should be compensated. They’re heroes, and Jade’s a hero," she said.