So the county has a rule...woodhaters..can you use steel studs?
Then some concreteboard or plywood?
The issue is your in hurricane central and they want you to be safe from flying 200MPH lawnchairs!!
Contact a builder or two in the area and see if there are alternatives they have tried. It may not be any cheaper than you learning some masonary skills and teaching someone else to help you.
Good luck on your bomb shelter!!!!