There’s a sale on Frontier through tomorrow, $15 fares for the fall on Tuesdays and Wednesdays. So if you can just book them even one way, it might be worth it. The tickets are $20 but use promo code SAVEBIG to knock it down to $15.
From Atlanta there are $15 fares to Austin, Cleveland. Cincinnati. Denver, DC, Indianapolis, Vegas, New York, Orlando, Miami, Minneapolis, New Orleans, Chicago and Philly