Wedding cost? Flat. Fewer marry. Wedding boom over?

Average wedding cost $25,600 last year, virtually unchanged from 2010. Many who are getting married are looking for ways to cut wedding costs.

When Allison Williams gets married in October, she'll be doing it on the cheap. At least, that's her goal.

"We're aiming for a budget of $10,000, but realistically, it will probably be about $12,000," she says of her upcoming garden wedding in Athens, Ga., with 150 guests.

Most of that $10,000 will go toward the outdoor cottage venue and the food, "because we've never been to a wedding with good food," she says with a laugh. Another top priority: good photography. "I still look at my parents' wedding album, so I wanted to make sure that part lasted forever."

Everywhere else, she and her fiancé are finding ways to cut back. As little as possible will be spent on flowers. Paper goods like invitations and party favors will be virtually eliminated. Dinner will be served on recyclable tableware instead of china. Her David's Bridal wedding gown cost less than $500 (about $700 less than the national average).

Ms. Williams's nuptials are a potential sign of trouble for the wedding industry. Fewer people are getting married, and those who are appear to be starting to pull back from the lavish affairs made popular during the 1980s and '90s. The boom that the industry has enjoyed in the last three decades – it pulled in $56 billion in revenue in 2011 alone – may be on the wane.

"I think many wedding companies believe the great boom generation is still coming," says Shane McMurray, founder and chief executive of The Wedding Report, a California-based marketing research firm that caters to wedding-industry professionals, in an e-mail. "But the smart businesses know the market has changed and the number of couples getting married is shrinking."

Marriage rates are going down: 20 percent of adults ages 18 to 29 are married, a steep drop from 60 percent in 1960, according to the Pew Research Center. The median marrying ages for women and men are higher than they've ever been: 26.5 for women and 28.5 for men.

And the average cost of a wedding has virtually stopped rising. Bridal-industry statistics can be hard to quantify because they're mostly self-reported and made up of surveys conducted by unconnected private agencies. Last year, average spending either stayed virtually flat (up $37 from 2010, according to The Knot, a top wedding-planning site aligned with WeddingChannel.com) or dropped $911 (to an average of $25,631, according to The Wedding Report). Aside from a blip during the recession, the average cost of a wedding has held steady in the mid- to high-$20,000 range since the early 1990s.

Two reasons for the shift: Couples are having fewer guests, and they have more money-saving resources at their disposal.

"Overall, current trends seem to be all about the money," according to the latest state-of-the-industry report from The Wedding Report. "Many vendors are seeing a decline in business due to couples opting to save money by going the DIY [do-it-yourself] route or hiring someone new to the business – or just friends or family members. Couples are more cost-conscious and are negotiating much more with vendors than they did in prior years."

That doesn't mean that weddings done the traditional way will get much cheaper.

"The budget was blown," says a groom who tied the knot in March in New Orleans (and declined to give his name). The couple's original $15,000 budget ballooned to $30,000 in a flash. He wasn't batting an eye over writing any check smaller than $700, he said. "Both from a planning side and an expenditure side it doesn't scale down that much. If you're doing more than a backyard barbecue, it's going to be expensive."

But the "traditional" wedding doesn't actually date back that far. As late as 1950, for all but the richest families, "the wedding was quite a small affair," says Carol McD. Wallace, author of "All Dressed in White: The Irresistible Rise of the American Wedding." "The upper middle class, those were the ones having the white dress weddings." For everyone else, "having a dress you wear only once was really startling." Before World War II, brides and grooms usually wore suits they could wear again.

Mass manufacturing combined with a new level of national prosperity began to change all that. But things really took off in the 1980s. "Two words: Princess Diana," Ms. Wallace says. "The '90s kept that going, and there was this arms race quality to it."

In 1984, the average wedding cost about $7,800 ($17,000 when adjusted for inflation). By 1990, the figure had ballooned to an inflation-adjusted $26,000, which is close to where it stands today.

For her wedding this fall, Williams is still going the white dress route. She commissioned a friend with a small graphic design business to make her invitations, and a co-worker is making her wedding cake, as a gift. She didn't hire a wedding planner, and is focusing her budget on things that will last. "The flowers will die. No one will remember whether you had $3 chairs or $1 chairs. Those are the types of things I didn't mind cutting back on."