Statuesque blonde Brandi Irwin, 28, sits in the salon chair, her long legs crossed, a pair of silver Louboutins dangling from her manicured toes. Behind her, a hairstylist tends to her locks with the precision of a Persian rug weaver.

The stylist plucks a silky bundle of hair from a nearby table and presses it against one of Irwin’s natural locks, squeezing the two pieces together at the root with what looks like a pair of hot pliers. And voila! The tendril has suddenly sprouted an extra 24 inches.

That’s one hair extension done — 250,000 strands (and nine more hours of work) to go.

Welcome to Gemini 14 on 14th Street near the West Village, home to the city’s most expensive hair extensions — which cost $10,000 a pop. Irwin has hers put in three times a year. Add to that her color sessions every six weeks at about $300 per appointment and $65 blowouts twice a week and she’s forking out roughly $47,000 a year to achieve her Rapunzel-like mane (including tips). In short, what most of us would pay for a car, Irwin blows on her crowning glory — every year.

“It’s my biggest expense,” says Irwin, a former-model-turned-foot-model and photographer from Park Slope. “But it makes me feel beautiful. And I’ve worked hard for what I have.”

Plus, she says, her parents invested in “some very profitable stocks, metals and things,” when she was young — meaning her family’s helping to foot the bill.

Irwin began lengthening her hair about six years ago when she worked as a fashion model. Since then, she’s become addicted. “I couldn’t believe it when I first saw myself with the extensions. It was the hair I’d always wanted, and it looked so real,” she says, stretching her long arms. The knuckles of her left hand are tattooed with the word “POSH” in black Gothic-style letters.

Gemini 14 salon co-owner Kristina Barricelli says the extensions are worth the price. Made from “virgin” hair donated by Indian women to Hindu temples as part of a religious offering, the strands are de-pigmented using a special “osmosis” process untouched by chemicals, leaving the hair as pure as possible.

Also, Barricelli says the hair company she buys from, Great Lengths, uses a keratin protein polymer bond to adhere the extensions, so they last longer, cause less damage and look more natural than brands that use tar, silicone and glues. The Great Lengths treatment lasts up to six months, she says, while ordinary procedures last significantly shorter and only look fresh for a month or so. Miley Cyrus and Broadway bombshell Kristin Chenoweth are both devotees of Barricelli’s extensions.

“It’s the Rolls-Royce of hair extensions,” says Barricelli. “Look, I don’t want anyone to mortgage their house for their hair. But if you can afford it, it’s the best you can buy. You’re guaranteed a perfect match with your hair color, with the best quality hair you can find.”

Dozens of other New York salons use the same hair extensions as Barricelli, but no one charges five figures. Most cost about $3,000, says Barricelli, adding she’s one of the most experienced practitioners of hair lengthening in the US — she’s been working with extensions for 10 years — and her prices reflect that.

Only about a dozen of Barricelli’s clients pay the full 10 grand for their hair. About 100 more come in for lesser lengths at lower prices.

But makeup artist Kate Bazazian wanted the lushest locks money could buy. “If you want to look like a million dollars, you have to spend 10 grand,” says Bazazian, 27. “If you spend 50 bucks, you’re going to look like you spent that. The cheap route will show.”

Bazazian had never been able to grow her coarse red hair past her shoulders. Now, thanks to the magic hands at Gemini 14, she has hair halfway down her back.

The Murray Hill resident spent $20,000 last year on two rounds of full extensions, but she now goes into Gemini 14 every five months for touch-ups at $2,000 a pop. She pays for them with a combination of savings and credit cards, hoping the sexy waves will lure new customers and keep the old ones coming back. “I feel like it’s an investment in my career,” said Bazazian. “It’s hard for me to justify to my clients that I will be able to make them look beautiful if I don’t look great myself.”

AJ, 28, who won’t give her full name because she doesn’t want to seem “high maintenance,” says she forks over the shocking price to avoid what she calls “the Kate Gosselin effect — when you can see where the hair ends and the extensions begin.” Plus, she says, “It just suits me more. My own flat, thin hair did not go with my personality.”

AJ says her family is in real estate, so they help — but she’ll also skip a bag or some dresses to afford the tresses.

“Don’t get me wrong — I have to budget. But I think it’s a plausible investment that I don’t mind making,” she says.

Back at the salon, it’s now 6 p.m. and Irwin’s mane is nearly finished. As Barricelli and her two sisters — also co-owners of the salon — finish blow-drying her curtain of fresh hair, Irwin unfolds all 5-foot-11 of her body out of the barber chair.

A waterfall of buttery gold unfurls down her back.

Irwin walks out on the street, strutting just a bit. Men stop and stare. They pull out their cellphone cameras, clearly wondering if Irwin is a star. “Is that Paris Hilton?” one guy asks another.

Irwin smiles with satisfaction. “Without the extensions people say, ‘Well, she’s cute,’ ” she says. “You add all this hair and it puts a ‘Who is she?’ factor on me. Without the hair, I’m this normal average person. But with it, I walk around the corner, and it’s like there’s a wind machine on me. It’s like I’ve stepped off the pages of a centerfold.”