Amazon is selling SM Stirling's "Conquistador" for $1.99 US.
https://www.amazon.com/Conquistador-...tador+stirling
This is an older book I read several years ago and enjoyed very much.
To quote a part of Amazon's description,
"Oakland, 1946. Ex-soldier John Rolfe, newly back from the Pacific, has made a fabulous discovery: A portal to an alternate America where Europeans have never set foot—and the only other humans in sight are a band of very curious Indians. Able to return at will to the modern world, Rolfe summons the only people with whom he is willing to share his discovery: his war buddies. And tells them to bring their families...: