In fact, some advisers feel clients may fare better, since special programs generally have no flexibility in penalties based on individual circumstances.

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An ultra-low-fare model gives carriers such as Allegiant and Spirit more flexibility in unbundling the costs of air travel, Cordle said, but other airlines will be watching the carry-on fee closely.

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The more flexibility they can offer, the lower the fare, which Mr Iacobucci says could be much the same as the price of a standard economy flight plus a night in a hotel.

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These are "meta search" fare sites, and although they don't offer quite the travel date flexibility as some others do, they often include fares that the airlines sell only on their own websites.

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