My next-door neighbor has a summer "pool bathroom" that's outdoors, sort of, but built into the house. They have to winterize it, of course, shutting off the water and filling it with pool anti-freeze every fall. No idea what it cost.
We don't but in an emergency it's just steps across a tile floor to bathroom off the kitchen--and it's a rough tile we put deliberately put in because it isn't deadly when wet.
Plus, after an hour, we get kids out.