Are you in the US? If so, you have a couple of good options. Sue over at Hollywood Poster Frames provides a quality product at a reasonable price. She will configure with non-glare plexi and acid free backing.
If you intend to swap out posters regularly, another good option is the front loading snap frames sold by Robert at Spotlight Displays. His system sandwiches the poster between 2 sheets of thin plastic and the frame snaps closed around it.
FWIW, plastic is recommended over glass for two reasons. First, glass breaks easily and can damage a poster. Second and more importantly, glass retains heat which will degrade paper. You can also purchase plexi and PET-G in UV resistant forms which helps with fading. Resistant is not the same as prevents and you still don't want to place posters in direct sunlight.
If you look around this site a bit, you will find many pages on framing and properly displaying your posters. Best of luck, and welcome.