Ilona Kaprovsky, a 24-year-old New Yorker who works in finance, said she didn’t initially think she wanted a diamond as the centerpiece of her engagement ring — a lab-grown stone like a white sapphire, or even cubic zirconia, would be just fine. Besides, who would know the difference?

But she eventually warmed to the idea when she and her boyfriend, Justin Veach, 28, started to talk about it more seriously. “During the process of buying the ring, we both were weighing what the value of the ring is,” said Veach, who is studying at Carnegie Mellon for his master’s in business administration and will probably finish with about $80,000 in loan debt. “Is it real? Does the diamond matter?”

In the end, it mattered, as it does for the many American couples who collectively spend billions on diamond engagement rings each year. In 2012 alone, they spent nearly $11 billion on diamond engagement and wedding jewelry, according to Olya Linde, lead author of Bain & Co.’s 2013 Global Diamond Industry Report. At a time when many young people are facing big student debts, a weak job market and rising housing costs, this luxury purchase still appears to be firmly planted on many ring fingers across the country.

The amount spent does tend to rise and fall with the broader economy, however, as it did in the latest boom and bust.

Couples paid an average of $4,000 on engagement rings in 2012 (and another $1,000 for her wedding band, and $500 for his), according to a 2013 report from Jewelers of America, a trade group, using data from a variety of jewelers. That is about 25 percent less than the average spent on engagement rings in 2006, or $5,317, before the economy collapsed, according to another report by the group. In 2011, couples spent $3,538 on average.

But arriving at the right amount to budget is something many young people continue to struggle with, and retail analysts say that more people are beginning to use the credit programs offered by the largest national jewelry chains. Thinking about how that money might work harder for you invested elsewhere clearly saps all the romance out of the process. And as someone who grew up spending summers working in her family’s small jewelry store, I am not opposed to celebrating the occasion, within reason, with something sparkly.

But let’s just pretend for a moment that you invested $12,700, or the current benchmark price for a high-quality 1-carat diamond, according to the Rapaport Diamond Index, an industry benchmark for diamond prices. In a portfolio of 60 percent stock funds and 40 percent bonds with a real return of 4 percent, that $12,700 would rise to about $27,830 after 20 years, and nearly $41,200 after 30 years (that’s after inflation), according to calculations by Vanguard.

If you invested an amount equal to the average ring price, or $4,000, the money would be worth nearly $8,800 after 20 years and almost $13,000 after 30 years.

It is hard to compare those values with sentimental ones, as well as traditions that are deeply embedded in the American psyche. Diamond prices are generally less volatile than those of other commodities, and the average annual appreciation of a high-quality one-carat stone is about 3 to 4 percent annually, according to Edahn Golan, an analyst specializing in the diamond industry. “Supply is limited,” he said. “It’s a millions of years process, and they are mined faster than they are being generated by mother earth.”

Of course, euphoric couples in love aren’t thinking about supply and demand (or that the growing middle classes in China and India are driving growth in the latter), nor do they view the ring as an investment. Even if they did, it’s not a terribly efficient value proposition, at least when you generally buy at retail and must sell at wholesale (and nobody initially plans to sell anyway).

A ring with a 0.7-carat diamond that cost $4,895 on Blue Nile, an online jewelry retailer, might sell for 20 to 25 percent more at an average brick and mortar retailer, while the same size and quality ring could command at least 40 to 50 percent more at Tiffany or Cartier, said David Wu, a luxury goods and beauty analyst at the Telsey Advisory Group in New York.

But what is interesting is that given how much has changed over the decades — men now snoop on their girlfriends’ Pinterest boards for clues about what they really like, and couples often shop together — the fact that it’s a purchase loaded with expectations persists.

I spoke with about a dozen 20- and 30-somethings in the market for a ring, with budgets ranging from $1,500 to $25,000, and many of them, mostly men, admitted that they were concerned about appearances, which factored into their budget: I feel like I should keep up with people in our circle, said one. Her family is wealthier than mine, wrote another. The perception is that I earn a lot of money and should be able to spend in the same way, added another, who is earning a healthy salary now but has been in debt in the past.

And the most popular refrain: She is going to wear it for the rest of her life.

Many of the young men and women I spoke with sounded relatively levelheaded about their spending plans — and the jewelers said that people tended to come into their stores highly educated on the topic and with a budget.

But others seemed to set budgets arbitrarily. One 27-year-old graduate student based his number — $1,500 to $3,000 — on what he could afford to pay off on credit. A 31-year-old lawyer decided to spend half his monthly income, or $5,000.

“I found that coming up with a budget is difficult,” said a 28-year-old consultant in Los Angeles, who wanted to remain anonymous because he had not yet proposed and did not want to make his concerns public. “It’s not easy to discuss.”