If you are a senior and have the federal parks pass, you will save much money on Federal campgrounds. If you want to stick close to the river however, there are few Federal facilities.
Pensacola, I highly recommend Ft. Pickens National Seashore campground.
The pass will save you lots of money at Ft Pickens however, as the day use fee you must pay is $16 for a week, nothing with the pass, and camping is half price. Chose campsites carefully as some have lots of low hanging limbs. Use Google satellite view to help you, AND Google Street View of the campground loops (yes, street view all the way around all the loops.) Stay away from loops B and D, no street view because of the limbs. These are only suitable for tents and popups.
Charles
