Once a luxury reserved for the privileged few, private islands are going mainstream. From the St. Lawrence River to the South China Sea, here's how to find an archipelago (or at least a cay) to call your own

From the vantage of a five-seat Piper Aztec, the white sand outlining Hog Cay appears to glow in the Atlantic shallows. Covered by tightly woven mangroves, the island looks like an untouched nature preserve floating in a pool of pale blue. But as the pilot swoops low—and so close to an airy six-bedroom house that I can see a teakettle on the stove—it's clear that this is no desert isle. In fact, Hog Cay, at the northern tip of the Exuma chain in the Bahamas, is perfectly habitable, and for sale: For $19.3 million, you can have the sprawling house and the surrounding 681 wild acres all to yourself.

Island shopping is an expensive pastime—our plane and boat rentals alone averaged $4,000 a day. Even so, real estate brokers say that business is brisk as a growing number of Americans look for an island to call their own. Of the world's 600,000 islands, only about 3,000 are fit for habitation and privately owned. At any given time, some 200 of them are for sale, ranging in price from $30,000 to hundreds of millions of dollars.

A Boom in Sales
"We're seeing an increased demand for private islands," says John Christie, a broker at HG Christie Ltd. in the Bahamas. He and many of his colleagues say that September 11 was a turning point in the market, with more Americans seeking isolated retreats after the terrorist attacks. April Newland, of April Newland Real Estate, on St. Thomas in the U.S. Virgin Islands, agrees. "My business has tripled in the last three years," she says. The day I speak to her, Newland is in a rush because a client is flying in from Texas on a private jet to look at Great St. James Island, a fully developed 157-acre haven with a big house and a tennis court. Its owner, a European who has used it as his winter retreat for 30 years, has just put it on the market. Asking price: $25 million.

Yet despite the lofty prices of many islands, they aren't the exclusive preserve of royalty and seriously rich commoners. In fact, for the price of a two-bedroom prewar co-op on Manhattan's Upper West Side—in other words, $1.5 million—you could buy a nice little landmass in Nova Scotia with a castle on it. Or, for less than the cost of a small parcel with a lagoon view on South Carolina's Kiawah Island—$346,000—you could enjoy solitude and lake views from your own five-acre island group in Maine's Branns Mill Pond.

The most active markets these days are the Bahamas, Canada, the Caribbean, Central America, Croatia, Finland, and, off and on, Washington State's San Juan Islands. "I have five listed," says Wally Gudgell, of Gudgell Properties in Eastsound, Washington. "That's a high number for me. On average, an island here sells about once every two years. The last island I sold went to Gene Hackman, who bought it from a couple in their eighties who were still commuting by boat." Gudgell, who raised his family on an island in the Pacific Northwest, says the region is unique in its isolation. "It's fairly remote already. To have your own island here makes it exponentially more remote."