I've got an airfare to Europe here...going once...going twice...SOLD to the fella in Philly with the Macintosh who already gave us his credit card number and can't back out now!

"Supply and demand" is a two-way street, and the Internet is the traffic cop who pointed that out to us. Auction sites have truly come into their own—witness the stupefying success and broad cultural effects of eBay. Bidding for travel is no exception—indeed, back in the old days (1998), its champion in shining armor, Priceline.com, was once of the true darlings of the Internet. Even Captain Kirk loved it! Well, Priceline is still around, and it has a bit of competition (see right), plus there's that variant on bidding sites called opaque fares, but we'll get to that in a minute.

First: online travel auctions. Simple. You give them your home airport, your destination, and your travel dates, they provide you with a deal up to 50% lower than official fares. The catch? You gotta be flexible on departure time and you don't get to pick your airline. Also, you have to brush up on the going rates before you get started.

The idea is you put in your itinerary and a price you're willing to pay, it lets the airlines (all the biggies are members of Priceline) decide whether to accept your bid and sell you a seat. Once you enter a bid, you are obligated to pay if an airline accepts the bid, so you have to be sure of this going into it. After all, they have your credit card number.

You also have to do your homework and find out the absolute minimum you could get a ticket for through regular methods. That means going through the whole rigamarole described on the "Getting the Cheapest Airfare" page. Then, armed with that fare, hack maybe 35% off it and plug that amount into Priceline. No, that 35% isn't scientific; I just made it up. It's a fairly reasonable rate—and yes, it's pointless to try and get a transatlantic ticket for $10—and you may get a bite.

Seriously: find out the going rate first. Whenever I go to these sites, I wince to see folks bidding ludicrous sums for trips that would cost them less if they just rang up the airline and asked for a ticket straight out—like bidding $250 for a round-trip ticket from NYC to London when the going rate at the time, on the very same airline, was $170. (Yeah, I know: great price. That’s what you can find on the sales page of Virgin Atlantic in the wintertime.)

Now you can always raise your bid if the first one doesn't get a nibble on the line. In fact, even if Priceline sends you a "counteroffer," don't take it yet. Just raise the bid a bit. Nine times out of ten, you'll get a taker before you ever reach the level of that counteroffer.

Note that you get the most restrictive ticket imaginable; you won't be able to change the dates or travel times, not even by paying the normal change fee. Also, you might end up with a circuitous routing. (I'd rather pay an extra $20 or $30 to fly direct from New York to Rome than be forced to waste an extra day flying from New York to Detroit to Amsterdam to Rome—which is a distinct possibility if Northwest/KLM accepts your bid.)

You can pull out before the bid is accepted if you get cold feet or feel the number is going too high. But once the auction closes or your bid is accepted, that's it. Your Visa bill instantly gets longer and your ticket goes in the mail (so to speak).

Opaque fares are not quite as loosey-goosey as auctions. You give an opaque fares booker like Hotwire your dates (departure/return) and cities (where you are and where you wanna go), and they give you a price to match. You pick the price you like (hint: it's the lowest one). Only after you pay the virtual piper do you find out the name of the airline and precise times of the flights.

There's nothing fishy about all this (well, not with the legit operations listed to the right). It’s just a way for airlines to move empty seats at amounts that far undercut their published fares without admitting that they're willing to sell seats for so little.

The two big opaque sites....

priceline.com - Though William Shatner no longer sings (poorly) its praises on national television, this darling of the dot.com bubble is still alive and well and accepting bids. Though you get to pick your travel dates and departure and arrival cities, you don't get to be picky about the times of your flights. For international, the airline that accepts your bid is free to assign you a seat on any flight from 5am on your stated departure date until 2am that night (well, technically the next day). To help you be vague so as to cast a wide net, when you enter your departure/arrival cities, Priceline will provide you with a selection of airports in or near your choice cities, and you can select as many as you're willing to possibly use (the more you pick, the greater your chances of getting that low fare). The airline that accepts your bid will tell you where you're flying from and to. Also note that the price you bid out will not include taxes, which can tack on an additional $85 to $115 (this isn't fleecing you; that's actually how much government taxes, security charges, airport fees, etc actually run these days), plus $6.95 for processing and, if you get paper tickets, $19.95 for S&H.

hotwire.com - Industry leader in online opaque fares, offering up to 45% off published airfares, 75% off hotel rates. Hotwire's 33 associates include founders America West, American Airlines, Continental, Northwest, United and US Airways. They also rep over 6000 hotels in 150 US cities and resorts. Unlike some bargain sites, they encourage you to shop around and try to beat their fares, and will hold a reservation free-of-charge for one hour. They also have some juicy last-minute deals. Hotwire was purchased in Sept 2003 by Barry Diller's insatiable InterActiveCorp (the same guy who owns Web travel powerhouses Expedia, Priceline, Hotels.com, and CitySearch plus other household-name business like TicketMaster, Match.com, and LendingTree.com), so be ready for possible changes—though Mr. Diller seems to operate under a "don't fix what ain't broken" mantra in companies he acquires; he just uses his clout to make them bigger.