Don't know if you are aware, but this site hosts auctions of the art and poster.  most originals from that time are going only for auction pricing.  You may want to have it authenticated by a reputable firm, so you can show the eventual buyer it is authentic.  Start here ==> http://www.wolfgangsvault.com/contact-us.aspx.

Full disclosure, I have no affiliation with this website of anyone at this site.