alt Hacker NewsCormac McCarthy appears to be an exceptional case in this respect. I skimmed through a book about it once. Early on he basically earned his keep through grants and book sales. I think he persuaded one of his old ladies to get a job while he wrote. And apparently he was always writing; pitching one book in the middle of working on another. I guess film and television soon followed.
Doesn't sound exceptional to me. Most of the authors I have some personal knowledge of manage through exactly that: spouses, grants, book sales, residencies and teaching creative writing.