As someone that has had similar problems finding good posters and frames, I've found that eBay has good deals on movie posters, especially if you buy a lot at a time and save on shipping. You just have to make sure that the poster is in good shape.
As far as frames go, you can go the expensive route listed above to go to FYE and get frames. I've found frames there for 15 bucks each, but they are the crappy frames that pull apart from all four sides, which actually makes it quite easy to change out posters. If you don't plan on changing them out, Wal-Mart has decent frames for 16 or 17 bucks a piece. Just make sure to get the dimensions of the posters. Authentic movie posters are 27X40 which is harder to find than the reprints (22x32 or something like that)