TALLINN, Estonia Ч It takes just 18 minutes to get here by helicopter from Helsinki, Finland. But only a fool would take a cramped helicopter, say visiting Finns. They pack a fleet of car ferries, stream here by the thousands every day, and have turned the visa-free, 90-minute crossings into an increasingly essential part of their household economies. ""How often do I come here? I think about making the trip every time I need a haircut,"" said Lauri Aalto, a retired teacher. ""The cost difference alone pays for the ferry."" Indeed, the economics are so compelling that, statistically speaking, every one of Finland's 5 million citizens visited Tallinn last year, on the 28 daily roundtrip ferry runs. In the Finnish countryside, feeder buses leave shortly after midnight to get to the ferry terminal for early-morning departures Ч carrying more than 6 million visitors a year. And why not? Gasoline here is one-third the price in Finland, prescription medicines one-half.