For kindle, Dune, cheap, at least for American customers.
Meanwhile, of possible interest: Other Worlds Than These by John Joseph Adams.
“We can all imagine such “other worlds”–be they worlds just slightly different than our own or worlds full of magic and wonder–but it is only in fiction that we can travel to them. From The Wizard of Oz to The Dark Tower, from Philip Pullman’s The Golden Compass to C. S. Lewis’s The Chronicles of Narnia, there is a rich tradition of this kind of fiction, but never before have the best parallel world stories and portal fantasies been collected in a single volume–until now.”
It is an anthology of some kind, I put it here because it looks interesting, but I’ve not read it. Have you?