If you want Lee Abbamonte, a travel blogger in New York, to plan your bachelor party, it will cost you $1,000. Actually, that's just for a consultation. To get him to make the arrangements will cost $5,000. Well, technically, it will cost $5,000 or 10 percent of the total cost of the event, whichever is higher. This is because, as he sees it, the bachelor party is "like a honeymoon for you and your buddies." And as with any honeymoon, says Abbamonte, 37, who caters mostly to Wall Streeters, the costs add up: "It can be $1,000 to $10,000 per person. It can be more if you get some rich guy who wants to treat his friends to some crazy weekend somewhere, and they all stay at the presidential suite. Then you can be looking at a six-figure weekend."

Vegas VIP advises partygoers to bring $200 to $300 for lap dances and $70 to $100 for drinks.

What was once an evening of debauchery—strip clubs, penis straws—has morphed into a longer, costlier affair. Now prenuptial gatherings often last three days and two nights, often in a far-flung location, says Kristen Maxwell Cooper, executive editor of wedding marketplace the Knot, which reports that 78 percent of brides and 75 percent of grooms celebrated last year with friends before the big day. "The shift came with the social media generation," she says. "They're more interested in experiences than things. It's not just about one night out at a bar."

Some of this may be explained by logistics. Millennials tend to move away from home after college, so bachelors and bachelorettes have friends spread across the country. Flying to a central meeting spot is almost always going to cost more than steak and a lap dance. But still! One survey in 2015 by Priceline found that 32 percent of 1,020 people polled had spent $850 or more on hotel and airfare to attend a bachelor or bachelorette party. Another, by the financial-services website GoBankingRates in April, surveyed 502 women and 503 men and found that men spend more than women on average on these outings. (Weddings remain more expensive for women—those dresses ain't cheap.) Groomsmen spend $681.13 on bachelor parties; bridesmaids pay $437.31. Even more striking: Best men commit $998.78, and maids of honor are in for $552.33.

Guys explain this imbalance by a shared commitment to the idea that life as they know it is about to end. "Men have a go-big-or-go-home mentality," says David Covucci, 32, an editor at the website BroBible, who's been to about a dozen bachelor parties. "They treat it as one last hurrah with the bros, where I don't think women see it that way." Abbamonte shares this opinion: "Guys see it as an opportunity to do something with their friends that they don't normally get to do."

Las Vegas is still where a lot of that "something" happens. But Eastern European hot spots such as Prague and Kiev in Ukraine have gained popularity among grooms-to-be, because the cities are "known for good night life and being pretty cheap," Abbamonte says. For almost-brides, Nashville has become the destination of choice. "When we were out one night on the main strip in Nashville, pretty much every major group of people we encountered was part of a bachelor or bachelorette party," says Emilee Deutchman, 27, of Jacksonville, Fla., who spent almost $1,200 on a bachelorette weekend in the Music City.

Can't afford that? Too bad, attendees say. Jill Mulligan, 29, of Brooklyn, N.Y., has taken money out of her savings account to attend a bachelorette party. She's never turned down an invitation because of cost, though. "Would I choose to spend my money this way on my own? Not necessarily," she says. "But it always ends up being really fun." Deutchman once declined an invite because of the price tag, and she says it led to hard feelings from the bride. For his part, Covucci says he's never said no to a bachelor party: "I'd rather be there and be unhappy about all the money I spent than not be there and be unhappy I wasn't there, with money I'd just waste on something stupid anyway."