since you're talking about a 50-100 yard gun, you can spend anything from $25 to $250, and still have a 50-100 yard gun.
For cheap, there's Leapers and NCStar (both China). Both have "100 yard" scopes in the $25-50 price range that actually work pretty good. Then there's always the variants of the Bushnell Sportview line for a small investment. Lots to choose from!