There's a balancing act when you decide to fly with a budget airline. You're balancing the desire to pay as little as possible with your desire to take a vacation that doesn't begin with you completely frustrated by a miserable flight.
Frontier is running a "Penny Plus" sale, and the fares are low enough to make that balancing act work. The sale title refers to tickets costing one penny plus taxes, and it's not a bait and switch. Frontier has $15 fares in both directions to many destinations. The round trip cost even shakes out to less than $30 often because of how the taxes work out. The below example has a $15 flight in both directions but costs just $28.42 round trip. Each route has different availability, but the dates are generally for flights between mid-September and mid-November.
The catch is the lowest of the fares are over relatively short distances. Examples of those trips include Atlanta to Cleveland and Dallas to Denver. But you'd probably spend more on gas driving the same trek than you'll pay for fares in this sale.
There are 28 routes that are genuinely "penny plus" trips and 102 routes with one-way fares under $50, including taxes.