Prom Ka-ching!

THE BLACK, midcalf lace dress that 19-year-old Alicia Gaitor modeled for her family and onlookers hit all the right notes. It was classic, yet fresh. Form-fitting, yet tasteful.

"I love it," her sister said.

"That dress was made for you," an onlooker agreed.

It was a great choice. But the look on Gaitor's face said it all: It wasn't the dress.

"She's always been picky," sighed her mother, Michelle. "Usually about the wrong things."

She and her other daughter headed back to the chairs they'd been keeping warm for more than an hour.

They were tired, but troupers. And why not - a high-school senior has the right to be picky about her prom dress, right?

That's why department stores all over the city are filled with teenage girls who are in a frenzy to find The Perfect Dress. Nordstrom, Macy's, Lord & Taylor, and . . . the Greater Bible Way Temple on 52nd Street in Parkside.

That's right, the typically nondescript basement of a church - where for three days last week, young women from the neighborhood scoured racks of donated dresses.

Other than being a time-honored adolescent rite of passage, prom can also be described another way: Ka-ching! Department stores dedicate floors to the pricey occasion. Nail and hair salons declare themselves "prom headquarters." "Make sure you look picture-perfect!" read a sign outside one Chestnut Hill hair salon.

But perfection doesn't come cheap. Going to the prom costs a student an average of $1,139, according to a recent survey. And in one of the nation's poorest big cities, where a family of four in deep poverty makes about $11,700 a year, that's a memory many just can't afford to make.

That's why four years ago, state Rep. Vanessa Lowery Brown started her annual prom-gown giveaway, which includes dresses, shoes, jewelry and beauty products. A local cleaner cleans gowns at a 50 percent discount. This year, they kicked off the event with a fashion show to show the girls that donated dresses could look just as good as, if not better than, ones with steep price tags.

"I was either going to have to find a really, really cheap dress at a store or not go," said 18-year-old Angela Hagins. Hagins admitted she had to be coaxed to the church by her mother. But by the time she and her friend Janiyah Brooks left, they had both scored. Brooks' dress still had the tags attached.

Around them, young women buzzed around the hundreds of dresses church volunteers carefully hung by size.

"Ooh that one looks like a Kardashian dress . . . let me try it on."

"What if I hold my breath, can you zip it then?"

"How about now?"

Volunteers fretted over the girls like personal shoppers with tips and support.

"Spanx is a girl's friend."

"A gold brooch would make that green dress pop."

"How are you doing in there?" Jenaye Munford sing-songed while knocking on the doors of rooms usually reserved for church business. Munford's self-professed love of shopping made her a natural adviser.

Except when it came to Gaitor.

With Gaitor's search nearly hitting the two-hour mark, and her sister asking for aspirin, two Mary Kay cosmetics representatives abandoned their table to join the hunt.

They got close with a showy silver number with a glittery top. It had the bling Gaitor had complained the black lace dress lacked. But it wasn't the one, either.

After entering the room with another armful of chiffon contenders, one of the cosmetic reps surreptitiously rushed in with a swathe of lilac silk. Even before the door closed behind her, you could hear Gaitor snubbing the shawl jacket that came with her pick. But minutes later, the cosmetic woman quietly emerged from the room empty-handed.

"I think we have it," she whispered.

"But let her make the decision," she quickly warned. Nothing changes an adolescent mind faster than too much adult enthusiasm.

As instructed, when Gaitor exited the room in the floor-length gown - without the shawl - everyone played it cool. But as Gaitor sized herself up in the mirror, no one seemed to breathe. She turned left, then right, then left again, and then suddenly, victoriously, she twirled.

"I love it."

Stunned, the women circled around her in support and clapped. Her mother and sister looked weepy with relief.

"Let's get out of here while she's still smiling," her mother said.