Low-fare airlines are crossing borders. Discount dynamo JetBlue Airways announced plans last week to start its first foreign route in June when it intends to fly from New York City to the Dominican Republic. Fares are expected to be as low as $268 round trip, vs. $423 currently on American Airlines. Low-fare carrier America West said last week it is adding more routes to cities in Canada and Mexico. Fares on flights from Las Vegas to Calgary start at $242 round trip. AirTran Airways, which is aggressively challenging Delta Airlines, starts fares from Atlanta and Baltimore to the Bahamas at $99 one way. Low-cost Frontier Airlines has become so successful flying to five cities in Mexico that it flies more passengers from Denver to Mexico than any other carrier. JetBlue has also applied to the U.S. government for permission to fly to the Bahamas, Bermuda, Canada and Jamaica.