They're at it again: Spirit pays you to fly

Spirit Airlines is a specialist in guerrilla marketing, with their 1 cent and 5 cent fares that can actually be booked. Recently, they've taken it a step further with "negative" fares, as in -$4 each way between Atlanta and Orlando. Naturally, these fares are only available on certain days, usually four in each direction, but they really are bookable if you're flexible in your travel dates. See the current list. This sale ends Wednesday Sept 18 at midnight ET.