Hello Seliamy,
Welcome to the forum!!
Give the auction archives at Heritage Auctions (ha.com) and/or emovieposter.com a try and see what things have sold for in the past to get some kind of an idea as to what your posters could bring at auction. You can also always try the completed auctions area on eBay to see if they have sold posters similar to yours in the past.
Good luck with your research and let us know if we can help!
2footlong / Jamie