ebooks.com has Stephen Brennan's
Classic Science Fiction and Fantasy Stories available for free. Be aware that it's mostly, if not completely stories in the public domain. Some of them are just excerpts of novels. The only review on Amazon (a 1-star!) complains that because there is no editorial content, it's hard to tell what is an excerpt and what is complete, and what makes these stories classic.
But hey, it's free! It's also not free at Amazon or Kobo.