It wasn't all through patronage though. I just finished listening to a biography of Leonardo da Vinci, and he was taught in a workshop, essentially as an apprentice. They would do independent commissions for people - portraits, statues etc. It's true that the great artists would get patronage once they were great, but it seemed that there were a bunch of these workshops with apprentices that copied the master's paintings, worked on commissions with them etc. Just thinking about it now as I write, and the Patronage is like the "made-it" moment where an artist gets rich, but I bet there were a multitude of apprentices that toiled away in workshops just making money for food.