Priceline sells you seats that would otherwise be empty. It costs almost as much to fly an empty airliner as it does to fly a full one, so airlines want the planes to be as full as possible. If you’ve got an airplane with 100 seats, and you’ve got 99 passengers, it would only raise your operating costs a by a pittance to put one more person on, and if you can sell that last seat for, say, $150, then that’s nearly $150 that you wouldn’t have made at all, otherwise. It’s the same marginal cost issue that ticker mentioned above.
No, I don’t know the exact numbers.