Whoops, I just now saw the question you asked me-sorry. A fair-priced lobby card from "Return of the Fly" usually runs between 20-35 dollars, depending on the scene involved.
Collecting Trivia: Lobby Cards were so named because they were posted in theatre lobbies in order to promote the films. Were almost always in a set of eight, and usually had various scenes from the film, although in some instances, they showed a scene (usually close-ups or poses of the actors) that wasn't even in the film!!
There were usually eight Lobby Promo Stills (almost always B&W)that were used as well, and usually had the same 8 scenes as the cards.
The British equivalent of set of eight shots from the movie were called FOH ("Front Of House") cards.