Frontier Airlines, which added many new routes earlier this fall, has brought back its 99% off sale. But you will have to move quickly, because the offer ends at midnight on November 13.
The cheapest tickets come over short distances, but there are deals all over. The best prices will get you flying round-trip for less than $50. The cost you're paying is largely categorized as taxes and "carrier imposed fees." You aren't getting 99% off of those.
All you have to do is drop in the code "SAVE99" at checkout. However, even if you miss the midnight deadline, it's worth digging into prices, because the airline has been offering good deals lately.