you can stay in Niceville or Panama City hotels for much cheaper than Destin. (Destin doesn't have many hotels, mostly condo's). Couple folks I know just got a room at the Days Inn in Panama City for next weekend for $60/night.
Camping at Henderson State Park, but it's usually full. Downtown Destin, almost across from Walmart.
"Camping on the Gulf" is a campground on Hwy98 just past the outlet malls on the beach side. it's more for RV's, but you could prob tent camp. commercial campground. located on the beach.
Topsail State Park is right on 30A right where you turn off Hwy98. camping there. state park, so chances are it's full also. send a PM to PhotoHikeDive as he's a ranger there and he might have an inside track on getting a space.
Rocky Bayou on hwy20 in Niceville (state park) is a place to check. it's just north of the mid bay bridge. often you can get a spot there when Henderson is full.
Grayton State Park over on 30a I think you know about.
St Andrews State Park in PCB is popular. (sometimes hard to find a spot). Same state parks the PCB jetties are in.
I'm sure Google can find more.