Does anyone know what I should expect to pay with such a limited time/area showing? Will these poster be more difficult to find and be more expensive?
Depends. There likely was a limited run of posters intended to be displayed in theaters. However, like most modern movies, there is a secondary market directly to people who want to hang one. Either done on large scale printers, or often on the same offset press used to make the originals.
Like Joerod said, this isn't hard to find if you are OK with a good quality repro.