PS, good, clean color lithos and etchings (aquatints) BY CHAGALL go for 15 to 30 K (numbered and signed originals.
Most of the posters had nothing to do with his personal attention like his line prints and crayon lithos.
Ive got a color etching of one of his thousands of versions of "I Villages"
(Thats a big series of works in which he celebrates his Russian hildhood by reproducing farm animals (usually a sheeps head) along with his face and the villageall distributed in the background.
Outside of his stained glass windows these are his most recognizeable.
I bought mine while Chagall was still alive and I was just beginning a career. I recall it cost a lot then but weve kept it in a room away from direct light.
Your color poster will fade because the ink technology hasnt really kept up with itself. The best way to keep a color print or a poster, is to use UV stable glass . I wouldnt display it like a watercolor or a painting, Id treat it like any other print, keep it from fading.
I see many Chagalls and Picassos (posters)at yard sales for anywhere from 5 to 20 bucks