Allegiant has round-trip flights from Austin (AUS) to Destin (VPS) for $86-$99, NONSTOP. Flights June to August. Departures on Monday and Friday. Weekends available. Origin/Destination reversible.
Allegiant is a Low Cost Carrier similar to Spirit and Frontier there are fees for a regular size carry-on bag. The maximum (free) “Personal Item” dimensions are 7 x 15 x 16 in, basically a messenger bag or very small backpack, but if you’re only staying for a beach weekend, you may be able to get by with a couple pairs of shirts and swim suits/shorts.