MEXICO CITY — The shotgun-wielding security guard buzzed Alejandra Aviles out of the pawnshop on the gritty outskirts of this giant metropolis. She left with a used cellphone she'd just bought for $90.

"It was cheaper than buying it new, and it works just as well," said the 38-year-old housewife, standing recently on a sidewalk next to a highway clogged with taxicabs, minibuses and 18-wheelers.

It wasn't her first visit to the shop, which belongs to First Cash Financial Services, an Arlington, Texas-based pawnshop operator and payday lender. Previously, Aviles pawned a video camera for $300.

Small change? Not for First Cash. The company has spent 12 years building a network of more than 420 Mexican stores that now generate more than half the company's revenue.

Its expansion has brought emulation: Austin, Texas-based EZCorp and Fort Worth, Texas-based Cash America International have invested in Mexican pawnshops of their own in recent years.

"Eighty percent of our store openings are in Mexico," said Rick Wessel, First Cash's chairman and chief executive. "As the quarters and years roll by, it will become more and more important to the overall picture."

First Cash and its competitors are hardly giving up on their U.S. operations, which have also been gaining ground. The weak economy has pushed many strapped Americans to take out short-term loans or pawn goods for cash. The rising price of gold is also a draw.

But analysts say the Mexican pawn business offers a juicy growth opportunity at a time when one leg of these companies' U.S. business — payday loans — is facing stricter regulation in some states (and potentially at the federal level) from what critics call crushing interest rates.

"The U.S. regulatory environment has created all kinds of headline risk," said Elizabeth Pierce, a financial analyst for Roth Capital Partners in Newport Beach, Calif. "What these companies have done is look for alternative forms of growth."

Mexico is one of the leading alternatives.

"The economics are better in Mexico," said David Burtzlaff, a financial analyst with Stephens in Dallas. "You've got a population base that is very unbanked, and some people use pawn shops almost as their banks."

Indeed, millions of Mexicans don't use banking services. More than half the nation's municipalities lack traditional bank branches, according to a recent report by the National Banking and Securities Commission.

Banks tend to focus on higher-income customers, said Carola Conde, an expert on microfinance and professor of public policy at the Autonomous Metropolitan University in Mexico City. That opens the door for alternative lenders.

"There are millions of people in Mexico with little or no access to financial services," Conde said. "With pawn credit, you take your radio, go to the nearest pawnshop and get money in 15 minutes. The big advantage is speed."

It'll cost you, however.

Luis Hernandez, a 42-year-old security guard, said he recently needed money for groceries. He went to First Cash and pawned his mobile phone for a loan of about $110. Now he pays a monthly fee of $20 to keep from losing the phone.

That works out to a financing rate of about 18 percent per month, or more than 200 percent per year. That's exorbitant for anyone used to U.S. credit-card rates, but it's comparable with the interest rates that many pawnshops charge in Mexico and many U.S. states.

As high as the financing costs are, pawn-loan fees accounted for only 27 percent of First Cash's revenue in Mexico during the first six months of this year. An additional 2 percent came from fees on consumer loans that are similar to U.S. payday loans.

The rest came from selling goods, with 16 percent of total revenue coming from scrap jewelry sales and 55 percent coming from retail merchandise sales.

In other words, a lot of the business comes from markups between what First Cash offers sellers (who typically need cash) and what it charges buyers (who often prefer cheaper used goods to pricier new ones).

Ten years ago, there were about 600 branches of for-profit pawn lenders nationwide, said Carlos Gomez, president of a trade group called the Mexican Association of Pawn Service Companies. Now there are more than 5,000, he estimated, most of them small shops dealing in gold and jewelry.

"There was regulation that created a good environment for investment," he said. "It was a business opportunity."