When I was traveling in Krakow, Poland, I was living on 10USD a day, including lodging, food (really awesome food), transportation and entertainment. I still don't understand how a train ride away the same lifestyle would cost 50USD a day. Why?
Because Dollars are in demand and Zlotys aren't. Look, money isn't "special". It's just a token of exchange. Supply and demand apply to it as to any other commodity. Dollars are valuable because you can trade them anywhere. The discrepancy is purely a premium for liquidity.