What's the price of infidelity?
How about $300,000? That's how much Christie Brinkley's soon-to-be-ex-husband, Peter Cook, allegedly spent to keep his 18-year-old mistress quiet. Feeling a little more frugal? Try $4,300 -- the price tag for former New York Gov. Eliott Spitzer's alleged night with a prostitute.
While Cook and Spitzer may represent extremes, they're not alone in opening their wallets to satisfy their extramarital appetites. Experts say that infidelity frequently manifests itself in sly spending on new wardrobes, dating Web sites and more.
"I really don't think a lot of people think of the financial aspect of it, but it's a huge part of it. I don't think you can cheat without it also being a financial betrayal," said Debbie Then, a psychologist and the author of "Women Who Stay With Men Who Stray: What Every Women Needs to Know About Men and Infidelity."
Ruth Houston, the author of "Is He Cheating on You? 829 Telltale Signs," estimates that between 70 percent to 95 percent of people who cheat on their spouses see their trysts affecting their bank accounts. That includes everyone from rich businessmen to people on welfare, Houston said.
"If a person is involved in an affair, there's money being paid somewhere along the line: to hide it, to initiate it, to maintain it," said Houston, who was once married to a cheater. "It happens at all economic levels."
Noel Biderman, the president of a Web site dedicated to infidelity, said some members of his site have reported that their affairs cost as much as $10,000 a year thanks to mundane expenses such as cell phone calls and cab fare as well as more luxurious spending, such as hotel stays and fancy gifts.
One man, Biderman said, spent upward of $40,000 a year to have flings with women across the country.
"If it was the right woman, he didn't care if she was from Missouri or Miami," Biderman said. "He was prepared to bring them in or go see them."
Spending on an affair has become easier to do since the advent of dating sites, Then said.
"You can sit in your office and do it. I think just putting it at somebody's fingertips makes it easier to do and easier to spend the money on," she said. "It's not like I'm out walking in a bad neighborhood looking at a strip joint."
Peter Cook's paramour was Diana Bianchi, a teenaged girl he had hired to work at his architectural office. Cook allegedly paid Bianchi to keep quiet about the affair through a $300,000 confidentiality agreement.
But Cook may have also taken his extramarital activities to the Web: During his testimony at his divorce trial last week, Cook said he was a member of AdultFriendFinder.com, a Web site that advertises itself as the "world's largest adult sex and swingers site."
The site allows members to create profiles, search other people's profiles, e-mail and instant message with potential mates, and view photos and videos posted by fellow members.
In comparison to his costly relationship with Bianchi, Cook's spending on AdultFriendFinder might have been a downright bargain. Cook said he had a "gold" membership at AdultFriendFinder that, according to the site, costs $149.95 for 18 months of access.
Among the benefits conferred by a gold membership: having your profile pop up at the top of other members' profile searches and access to "extra large" photos.
AdultFriendFinder, which is owned by Penthouse magazine publisher Penthouse Media, allows members to list themselves as "attached" or "married" -- as well as "single," "divorced" and "widowed" -- on their profiles, an option implemented after users suggested it, said Penthouse Media Chief Executive Marc Bell.
But the site doesn't encourage infidelity, Bell told ABC News, any more than sites like Facebook and MySpace do.
"It's just another social networking site," Bell said.
The same can't be said for AshleyMadison.com, the online dating service run by Noel Biderman. The Toronto-based agency makes no bones about the service it provides. In fact, the slogan topping its home page reads "Life is short. Have an affair."
Biderman said AshleyMadison.com was founded in 2001 to meet the needs of married people who were trolling singles' Web sites in search of extramarital mates. The site, Biderman said, has seen its membership double over the past year to more than 2.2 million.
For $49, members can create profiles and send a limited number of e-mail and instant messages to potential mates. The more e-mails and messages you want to send, the more you have to pay.
Biderman said most men find success with the site's $49 package, but some choose to upgrade to pay for more messages. Because 65 percent to 70 percent of the site's users are men, Biderman said, heterosexual male users typically need to send out more messages before successfully wooing a woman.
Women, Biderman said, make just 5 percent of the purchases on the site.
"The site is definitely designed to monetize the men and validate the women in that regard," Biderman said.
While most male members have had success with just a $49 package, Biderman said he also knows members who over the years have spent thousands of dollars to have multiple affairs.
AshleyMadison.com isn't the only option for Web-savvy cheaters. PrivateAffairs.com allows infidelity-minded users to place personal ads for a monthly subscription fee of $29.95, or $109.95 for a year.
The site advertises itself as a serious place. According to the Web site, it includes"[n]o game players; only qualified people seriously seeking an extramarital experience."
Even if a relationship appears to take place only in cyberspace, Houston said it can be just a matter of time before a would-be cheater turns his online hookup into a real one.
"If you're not changing partners, if you're not corresponding with different ones, it's always with the same person, sooner or later, you're going to want to meet that person," she said. "That's when it really begins to take a downward slide."
When things do get physical, the amount an adulterer shells out, she said, can vary depending on the type of relationship. While a one-night stand's expenses may be limited to just dinner or a hotel stay, she said, someone involved in a long-term affair might make purchases with the intention of improving their own appearance.
A cheater might spend money on a new wardrobe or a gym membership to impress his or her new mate, Houston said.
"He's gone overnight from Kmart to Armani -- there's something wrong with that," Houston said.
Biderman said that when it comes to affairs, there are also those who pinch pennies.
He said one member of AshleyMadison.com has had five or six affairs going at once, yet he is adamant about "never spending a dime." What he offers women, Biderman said, is his attention.
"That's his approach, and he seems to be wildly successful," Biderman said.
Houston said those who do shell out big bucks on their affairs often leave a paper trail. Tax returns, she said, can prove especially revealing: They can alert a spouse to bank accounts they didn't know existed or to the sudden sale of stocks, profits from which, Houston said, might be used to pay for extramarital expenses.
Houston said that cheating spouses will often hide credit card statements from their partners. If you do have access to your spouse's bill, Houston recommends checking for gift purchases, especially around Valentine's Day.
"If he's buying gifts for females, is he really buying $300 worth of lingerie from Victoria Secret for his mother?" she said.
"You don't want to be come paranoid," she said, "but you do want to be aware of the types of things that could indicate trouble."