Around 1980, when I lived in Ashland, Oregon, there was an occult bookstore downtown called The Golden Mean. A Christian bookstore opened across the street and the folks named it Bread of Life after considering The Golden Nice.
Kidding about cult stores aside, the best example of a true cult author likely to interest some people here could be Phyllis Paul. Except for Twice Lost (happily, possibly her best, and at present back in print), her books are generally hard to get hold of and hardly anyone has heard of her, and of those who have, many, presumably, have not been able to read her books. I have two of her books as books (Lancer paperbacks aimed at the Gothic market); the other nine are photocopied (by me) from the US Library of Congress, the National Library of New Zealand, etc. Getting these books to copy took me and an interlibrary loan librarian some months. Chrons has two threads about Phyllis Paul, for those interested.