A couple of great book bundles are available:
Women in Fantasy which is curated by Kristine Rusch and has 5 books for minimum of 5 dollars and 10 books for minimum of 15 dollars, among them Rusch, Judith Tarr, Laura Anne Gilman, and one Fiction River short story collection. 6 days left to buy
Storybundle has two others bundles, too: Gaming books and True Crime.
Meanwhile Humble Bundle has a group of Sci-Fi classics (Males in Sci-fi?) including Zelazny, Asimov, and Bester. (Personally I wouldn’t call Betancourt’s Amber prequels classics.) 12 days left to buy.