I recall reading one of Fred Picker's newsletters, where he spoke of answering a letter he'd received from a customer. The author of the letter wanted to know if Picker could tell him how to "get into the business of fine art photography."
Picker's reply was, "There is no such thing as the business of fine art photography." He ran a photographic supplies business to finance his personal work, and I think that's true of almost all fine art photographers.
Michael A. Smith and Paula Chamlee are the only people I'm aware of who make their living from the sale of their prints.