The stamp is RB31p, the hyphen hole perf variety of the 5¢ Battleship proprietary. it has a current Scott catalog value of $25.00. However, with a tear at the top, poor centering, and soiled in the front, your copy would attract few collectors of the battleships. Condition is really quite poor for this series of stamps.
The stamp I am using is from Altoona, Pennsylvania. The inverted denomination remains the only one with the inverted denomination that has surfaced to date.I am sure that there must be some sitting on deeds, but they have not yet found their way to the philatelic marketplace.
Unfortunately in stamps scare and valuable are often not synonymous. The British Guiana 1 cent sold for over a million dollars and it's one of a kind. The stamp above even though it is a one of a kind probably won't fetch $50,000 simply because there is the other side of supply and that is the demand.