These prices are only available when you book TODAY for travel through Feb. 2010. Flights at these prices are available on specific days. Become a Spirit Airlines member for $40 and these fares are slashed in half. A 60-day trial membership is $9. No joke.
Okay, clearly Spirit Airlines is pegging the sale to what I'm guessing is its hub, Ft. Lauderdale. But not all the sale flights involve this airport. See all the sale fares here.
Caveats: specific flight days are required to get the sale prices, sale prices based on round trip purchase, fees apply, first checked bag is $19-$25.