Yeah I'm going to go with the general concensus on this one.
Your doctor will say "why do you need diapers?" And you answer is? "I pee myself uncontroably"
At that point the doctor will look to see what's wrong inside, will prescribe medecations first, and probably as a last resort actually write a prescription for diapers.
I personally wear them for fun, and I don't do it all the time, so for me $30-$40 every couple of months on diapers is fine for me.