Flood Plain Craziness - Do I really have to listen to the county here?
Since in commentary you've stated that you're already committed to genuine flood-resistant construction, now it's just a matter of documenting that to the satisfaction of insurance companies and the county. 

My advice is to research the gold standards in flood-immune construction, and modulate your design so that it plainly conforms to that.  I don't think you need to go to the extreme of stilts; it just needs to meet whatever standard they will be satisfied with.  

The new designs being used in the Gulf Coast are just basically stilts but in the form of continuous poured concrete walls.  Flood remediation is one of those scrub-brushes you attach a hose to, and down the drain/out the door it goes.  

As far as insurance, just because you're cash-building this one, doesn't mean you can afford to cash-build its replacement (A flood may not ruin it, but fire would).  Also, insurability means resale value, and even if you don't see it, your heirs will.