GREAT BARRINGTON, Mass. -- Diana Felber brought her groceries to the checkout and counted out her cash -- purple, blue and green bills that are good at only businesses in western Massachusetts.

Known as "BerkShares," the colorful currency is printed by a nonprofit group to encourage people to spend close to home in the state's Berkshire region. Customers who use the money also get a built-in 10 percent discount, since they can get 100 BerkShares for just $90 at local banks.

"I like all the ideas about local," said Felber, 64, an artist shopping at the Berkshire Co-op Market. "I also like that it's a discount. Who wouldn't like that"

The BerkShares program is one of the most successful of its kind in the country, and it is attracting attention as other communities look for ways to insulate their economies from the deepening financial crisis.

Susan Witt, co-founder of the nonprofit Berkshire Inc., said her group receives about three calls a day from other people interested in creating local currencies.

So far, more than $2 million in BerkShares have circulated through 350 businesses since the bills were first printed two years ago.

BerkShares look similar to real money for good reason: They are printed on specialty paper from Crane & Co., a local company that has been the sole provider of paper for U.S. currency since 1879.

The bills come in denominations of 5, 10, 20 and 50, and feature portraits of well-known local figures: a Mohican Indian, the original inhabitants of the area; civil rights leader W.E.B. DuBois, who was born in Great Barrington; community leader Robyn Van En, who died in 1997; Herman Melville, author of Moby-Dick; and painter Norman Rockwell, who lived in Stockbridge.

National retail chains in southern Berkshire County have not signed up to accept the currency, and BerkShares cannot be traded online with out-of-state merchants, Witt said.

"I'd much rather take BerkShares than you giving me your credit card," said Steffen Root, co-owner of Berkshire Bike & Board, citing card processing fees. "I think that we can keep our money local, it's a good thing -- especially with our economy, where it's going."

Interest in local currencies often spikes during a recession as communities scramble to promote their businesses and curb unemployment, said Lewis D. Solomon, professor at the George Washington University Law School and author of "Rethinking our Centralized Monetary System: The Case for a System of Local Currencies."

The U.S. Constitution prohibits states from coining their own currency, but it is silent on local paper money. The courts have allowed private groups to print complementary currency, provided it does not compete with federal money and does not circulate beyond a limited area.

For accounting purposes, the Internal Revenue Service requires that income received in BerkShares and other local currencies be declared in U.S. dollars.

The Massachusetts program is one of several local currency systems, including those in New York, California, Kansas, Michigan, Oregon, Pennsylvania and Wisconsin. One of the oldest is Ithaca Hours, which went into circulation in 1991 in Ithaca, N.Y.

"If you have local networks, you can trade within them," said Paul Glover, founder of the Ithaca program. Whether they are business, religious, neighborhood or professional groups, "there is a capability within those to trade without strict dependence on dollars."

Starting a local currency isn't cheap.

In the Berkshires, Witt's group spent $250,000 in grant money to pay for research and development and to create the alternative financial system. The group has made its research available for free online, hoping to help reduce costs for other communities seeking to set up a similar program, she said.

The bills are traded an average of four times before finding their way back to the banks, Witt said.

Not everyone is a fan of the local currency.

Machal Snyder, a bookkeeper for several businesses, said he stopped going to the bank to get BerkShares.

"I just started using my debit card for everything," he said. "I hate to admit it, but I think that I have become a bit more about convenience."

Those concerns may be resolved by an expansion program that includes branching into debit cards and offering loans to business startups, Witt said.

Shanace Sullivan said BerkShares help her support relatives tied to the local economy.

"A lot of my friends and family are people who work in the local trade, so it's important for me that business stays in the area. And any business that I have, I can try to keep it here," she said.