This sale is good for just $24 hours when you use promo code 24HOURS. You always get $10 off on Spirit when you book on their site, so this gives you an additional $14 off. Plus, you save booking fees that you'll encounter on sites like Travelocity (typically $7) for a total savings of $31 round-trip. Right now, we see a lot of $104 RT fares on their nonstop routes, such as New York/Detroit, Detroit/Ft Lauderdale, and Chicago/Tampa. Meanwhile, Northwest is beating the sale by a few bucks out of Detroit.