What movie posters do you see for $10?
Theatrical one sheets can also go for quite a bit of money (eventually) depending on the film and poster. I have many that are worth thousands of dollars, and many more that are worth hundreds of dollars.
In the end it is like any other collectible, to someone else, they see it as just a piece of paper and not worth the money, just like some look at Sideshow or Hot toys figures and just see an over-priced piece of plastic.
It's all in the eye of the beholder.
Edit- there is one set I would love to have, I forget the artist but they are Star Wars themed, C-3PO representing Tatooine, Fett representing Bespin and Vader for Endor. I really want those posters, but for the price I cannot rationalize buying them.