An excellent Western with a Horror bent, Bone Tomahawk is worth paying to see, so watching it for free is as much of a no-brainer as it gets.
We always advise people (who live in North America) to subscribe to Amazon Prime. We do it for the Free 2-day Shipping (which pays for itself after about 10 orders), but they also have plenty of movies, TV shows, and music to stream for free, which is a nice little bonus to the whole thing.
If you're already a member, then go and check out Bone Tomahawk for free, right HERE. If not, and if you regularly order all kinds of things from Amazon, then sign up for Prime below, and never look back.