The Mists of Avalon by Marion Zimmer Bradley.
Not sure how hard it would be to get, being that the copy I have was my mothers that she got in 1982. Oops?
876 pages in paperback (all four books). It follows the tales of King Arthur, Morgaine (Morgan le Fay), Gwynhefar, and so many other amazing personas.
It is a rough book to read, I do admit, and I don't recommend it for anyone under 13 or so, being it has some suggestive themes.
I'm not sure if they sell in separate books, being that I have the copy that holds all four together. Meh.