Priceline.com

(CNN) -- How would you like to tell the airlines how much you want to pay for a ticket? Even if a last-minute business trip comes up, you may still be able to save by bidding online. It's called "ticket auctioning," and it's giving travelers yet another option to find low airfares.

Once such Web site is Priceline.com. You've probably seen or heard the ads from spokesman William Shatner. The site courts the leisure and the extremely flexible business traveler.

"You're naming the price you want to pay, and let us find an airline with empty seats where they'll release a seat at that price," says Jay Walker, Priceline.com's chairman.

The site works best for reservations inside of 21 days of departure. You can't choose the airline or rack up frequent flyer miles. And you must commit to at least one lay-over.

Another service, Travelbids.com, acts as a reverse auction. You book a reservation, but don't pay for it.

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"The traveler then lists the travel on the Travelbids Web site and then many travel agents have the opportunity to bid on their business," says Travelbids.com president Hal Segal.

Licensed agents from across the country bid, within a time limit you set -- from one hour to 72 hours. A 6 percent discount is guaranteed, and some are as high as 12 percent. You'll pay $5 for each Travelbids request.

Priceline is free, although a re-submitted request for the same trip costs $25. And once a request is approved, your credit card is charged. No refunds.

Travelbids.com

Intriguing as they sound, travel auctions aren't for everyone.

"The confusing nature of the sites and the restrictions that are involved make it only ideal for a very small percentage of travelers," says CNN business travel consultant Chris McGinnis.

Dr. Glenn Miller put in a bid on Priceline.com from Baltimore to Tampa, Florida. Although his request was denied, discounts and the freedom of the Internet will keep him coming back.

"It makes me feel like I have more options than just, you know, calling the airlines or calling the travel agent," Miller explains.

Airlines benefit, too. Each year, they fly half-a-million empty seats, so they're hoping more Internet surfers will help to fill up the skies.

Based on a report from CNN's Business and Travel and Beyond. The segment appears weekdays on Early Edition at 7 AM (ET) and on Morning News at 10 AM (ET).