Finding right airfare isn't a big investment

Shopping for a plane ticket online can be a little like following the stock market. Prices can fluctuate from minute to minute depending on how much demand there is for different seats, making it difficult to determine the best time to buy.

Anne Banas's strategy is to start looking early. Banas, the executive editor of SmarterTravel.com, a consumer website in Charlestown, begins looking at flights three months in advance to get a sense of what seats are selling for, a practice she calls "benchmarking."

Then she'll be able to tell when the price comes down and can make a more informed choice about whether to buy.

"You can't always ensure you're going to get the cheapest price, but you want to get it at a price you're going to feel good about," Banas says. SmarterTravel.com has a related site called bookingbuddy.com, which links consumers to several airfare websites, such as Travelocity and Expedia.

To help you track prices over several days, Kayak.com, a Connecticut travel website that compiles information from 120 airfare vendors, generates graphs for different flights. But Keith Melnick, the company's executive vice president of corporate development, still cautions against waiting for a huge drop in price.

"The earlier you can book it the better," he says. "Ninety-five percent of the time, the prices go up."

Experts recommend buying tickets at least 21 days in advance, or as soon as possible if it's an important trip. Melnick says he will buy tickets as soon as he knows he is going to travel. The best deal he's ever found was a flight from London to Rome on European low-cost carrier Ryanair for 1 pound, or about $2. With fees, the price was still only about $40.

But those who are looking for a spur-of-the-moment vacation can sometimes find good deals at the last minute if an airline is trying to get rid of seats. Banas recommends checking out weekend flights on Tuesday night or Wednesday morning, and SmarterTravel.com offers a listing of last-minute deals.

As for which days to fly, experts offer some different advice. Michele Perry, director of communications for Needham's TripAdvisor.com, notes that midweek travel to vacation destinations can be cheaper.

But Melnick says leisure travelers might want to avoid Mondays and Thursdays, which are peak days for business travel. Both he and Perry recommend flying on Saturdays, when demand is low. Fares, especially on international flights, also can be less expensive if they include a Saturday night stay, Melnick says.

Kayak.com and other sites such as Travelocity.com, Orbitz.com, and Expedia.com allow you to search flights on different days to find a lower price. If you want to expand your options to find a bargain, these sites often will allow you to search multiple nearby airports. This can save you, for example, $50, but experts caution that a $50 difference in price might not mean much if you have to drive farther to get to the airport and park.

Melnick notes that demand for air travel was up in 2006, and believes that trend will continue in 2007. Since airlines can count on filling their flights, that could mean fewer fluctuations in price, and more incentive for travelers to book early.

"When demand is up, airlines can do a better job of managing their loads and capacity," he says.