Island-Buyer's Checklist

1. Location, location. Even more so than with waterfront property, the price and convenience of island life is affected by its proximity to a mainland marina with groceries, parking and medical care. So unless you plan on living like Robinson Crusoe, an island's location should be your first shopping criterion.

2. Of bugs and men. Farhad Vladi, a broker who has sold about 2,000 islands since 1971, notes two key questions island-shoppers often fail to ask before buying: What's the local crime rate? And what's the mosquito and bug situation? "When I see white-sand beaches, that's a red flag to me that there are too many sandflies," says Vladi.

3. Four-season appeal. Vladi also recommends that you make sure your island will be pretty and accessible year-round -- a point that might seem obvious but isn't to some buyers. Visit your property at low tide to make sure it's not surrounded by mud flats. Islands with coves that are naturally protected from surging water are ideal.

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4. Permit problems. Before you buy an island, make sure to ask the authorities what you can build on it -- if anything. "Islands without building permits are literally worthless," says Vladi. Once you own an island, you may need permits for simple activities, such as lighting an outdoor fire. Fees will range from $10 to $100 a permit.

5. Building budget. Offshore building generally costs twice what it does on the mainland. One reason: Renting a barge to move heavy items can run $20,000 to $100,000 a month. Also, materials must be more durable and are therefore more expensive. Installing a septic system and a power generator may add up to $100,000.

Next: See our slide show of ten private islands for sale.

And: If you're not ready for a long-term commitment, consider renting an island.