Episode 1 double sided theater poster...Anyone know how much it sells for?



Hello gang. I was lucky enough to score an Episode 1 theatre poster when the movie came out from a close friend who managed the theatre at the time. It measures 27x40 and is double sided for lightbox display. I have been selling a few pieces from my collection lately and was wondering how much this poster goes for on the secondary market. I searched online but basically found nothing to give me an overall average of price. Any help from you guys about an estimated price would be appreciated.