What is the original price of a 1890 revolver?

Depends entirely on the revolver- make and model. In 1890, a Colt Single ACtion Army was ABOUT $25.00, depending on caliber, barrel, and finish. However, there WERE very cheap revolvers selling for less than a dollar. See if your library can get you a reprinted copy of the 1896 Sears catalog. it has a whole section on rifles, shotguns and handguns that were for sale (by mail!)