Original Batman Movie Poster

My grandmother won this poster from a Warner Brother's Movie Club drawing in 1989.

I have the original paperwork from Warner Brothers and the shipping receipt. They had the poster hand delivered.

This poster was the one that was displayed in Warner Communications Building at 75 Rockefeller Plaza.

It's on 48" x 66" plexiglass that is 1/2 an inch thick.

I am wanting to get an idea of what it's worth and how to get in contact with Batman collectors.