Bonita Springs which is south of Ft. Myers, north of Naples. Smaller town 30-40 minutes to either either city.
Highway #41 is the main road north/south so expect some congested traffic especially in season.
Look into the gated community "Pelican Landing", nice amenities, work out room, private beach(recently overhauled), tennis and golf. Probably less $ than Sanibel, Captiva, Marco Island probably more $ than Ft. Myers area or Tampa area.
You might also look into the area west of Tampa/St. Pete. Pinellas Park my Aunt and Uncle winter there every year and love it!
The further south you go the cost of living increases.
Sarasota is another very nice place, I very much enjoyed the half price used book store.
I so miss Florida!!! Despite the No-See-Umms eating me alive.