To flexible flyers, great deals are smooth sledding

If you're thinking about booking an airline ticket as a holiday gift, it's important to realize that purchasing airfare is definitely not like buying tickets to a play.

Let's say you're at the box office, and you're told that the performance you wanted to attend has already completely sold out. There's a possibility that tickets could become available at the last minute, but unless you go to a broker, you're not going to be able to get a seat for the sold-out show just by paying more.

However, if you want to fly from Chicago to Miami on the day before Christmas, even if the cheapest seats are already sold out, you can still buy a more expensive ticket. That's because airlines offer a wide range of prices for the same seats. A flight that sometimes runs as low as $200, for example, might cost you $300 or more if the lowest "fare class" isn't available. By waiting until someone else has snagged those cheap fares, you've ended up spending more for the exact same service than the guy sitting next to you. And in my mind, that's a waste of money.

That's why it's always a good idea to book your tickets as soon as you solidify your travel plans, assuming there are low prices available at that time. And if you're truly interested in saving money, the single best thing you can do is to be flexible with your travel dates. Not only do prices start lower on some days of the week (depending on the airline and route you're flying, it may be cheaper to go midweek, or on Tuesdays, Wednesdays, or Saturdays), but by being flexible, it's more likely you can travel on a day when the lowest fares haven't already sold out.

But how do you know if traveling a day earlier or later might cause the price of your ticket to drop? The good news for consumers is that more and more airlines are introducing flexible-date searches that mirror a similar service Orbitz launched in 2003. In the past month, both American and Air Canada have rolled out versions of this feature, joining a select club of airlines that includes America West, Continental, and British Airways.

Both American and Air Canada should be commended for making it extremely easy to learn which days are the cheapest to fly. When you choose the flexible search on American's website, you select a date range of up to 31 days and specify whether you want your trip to include a Saturday-night stay. A list of possible fares is returned to you, and you can then pick dates from a calendar when those fares are actually available for purchase.

Air Canada offers the flexible search whenever you shop for an airline ticket. You can see the cost of choosing a particular flight on your preferred days, along with the lowest possible price for travel on any other day that week. Let's say that you originally planned to fly Monday, for a fare of $200. When you price your ticket on Air Canada's website, it's easy to see that you can travel on Thursday for just $78. And then, when you select Thursday as your departure date, you can quickly tell exactly which flights will get you that fare. That's the kind of transparency that more airlines ought to strive for.

The alternative to flexible search is trial-and-error. Go to Delta's website and you can never be confident that you're getting the best fare in the marketplace. Rather than entering different combinations of dates until you find something you're satisfied with, you're better off using a site where you can compare fares - especially one where you can see that traveling on different dates might save you money. Stay flexible and it's likely you'll even be able to afford a pair of premium Broadway tickets. Just be sure to buy them before the show gets sold out.