Taking a page from the SkyEurope playbook, Spirit Airlines is offering a deal where they’ll pay you up to $4 to fly (you’ll have to pay taxes and fees). Only a handful of dates are available for each city pair, but you can construct round trip flights where you’ll just pay taxes minus $8. Cute gimmick.
FOLLOW UP: Now this is interesting: that page and that promotion have disappeared from their website. One of two things happened: 1) Technically, they were having trouble with negative dollar fares (entirely plausible); or 2) Some regulator called and told them they can’t say that they’re paying you to fly when, because of taxes, you’re still paying to fly. While the first is highly possible, I’m going with number 2. Any updates are appreciated.