Parents whose kids are clamoring to crawl the trick-or-treat route as Spider-Man or prance like Cinderella this Halloween will have to shell out $30 and up for officially licensed costumes.

The thrifty are turning to costume swapping -- through parents' groups, community centers and the Internet.

"Since we don't use them much, why not swap them?" mused Jonni McCoy, Colorado Springs, Colo.-based author of "Frugal Families: Making the Most of Your Hard-Earned Money" and other money-saving tip books. "It's a great way to go."

Typically a group of parents meets to trade, starting as early as September to ensure time to find costumes if the swap yields nothing. Sometimes parents will pay a small fee for a costume or for shipping if swapping online.

The San Carlos/Belmont Mothers' Club of California held its first swap last month. Parents brought at least one costume to trade in for tickets, which granted access to tables of costumes grouped by age. Leftover costumes went to charity.

Board member Pat Cremer said the idea arose from the group's traditional "Swap and Sale ," where members trade or sell baby clothes and other wares. "There is a good demand for gently used baby items. Halloween costumes seemed to be a natural extension," she said.

And swapping helps clean out clutter at home.

"People have costumes hanging around; their children have outgrown them," said Karen Coupal, 32, of Kenmore , N.Y. , whose Buffalo area Mothers & More chapter also held a swap last month. "A lot of people don't want to go through the trouble of selling them."

While exchanging costumes can be easier than hawking them, cutting costs remains the driving force.

Halloween is "big business now," said Lois Eannel, who heads youth services for the Palm Harbor Library in Florida , which sponsored a swap this month. "It's become hard for some parents to compete."

That point can be especially significant for families with several children.

"I'm not crafty, and with four kids 6 and under I don't have much time to make a costume that fulfills my kids' specific wishes," said Amanda Witman, 31, of Vernon , Vt. , who started a Halloween swap last year on www.yaaps.com, which stands for Yet Another Alternative Parenting Site.

Last year, "a mom generously gave me two Superman costumes in the right sizes for my boys, free for shipping," Witman recalled. "This year, I got a Spider-Man costume for my 4-year-old and a pumpkin costume for my infant, both from different moms, for the cost of shipping. I also found a home for the monster costume I spent $15 for" at a consignment shop.

Parents who want to start or join a swap should consider the possible pitfalls, organizers say.

For online swaps, "the only drawback is the trust factor: Do I send them money? Do I get my costume?" and is the costume as advertised, cautioned Amy Schamburek, 31, of Sheboygan Falls, Wis., a mother of five who started a Halloween swap six years ago on her Web site, www.20ishparents.com.

Schamburek said online swappers are more likely to trust a parent who regularly posts to an online community over a newcomer.

For in-person exchanges, there are other considerations.

Rebecca Riccio, 38, who arranged a swap this month for the parent-teacher organization of John Q.A. Brackett Elementary School in Arlington , Mass. , said swappers should know that participating is a gamble. In a group trade, where costumes are placed together, parents might end up forfeiting costumes without finding suitable replacements.

"If you feel highly invested in the costume (brought to trade) or you're hoping to find the perfect costume, you shouldn't do it," Riccio said. "There is a certain amount of risk involved in the whole process."