A digital postal scale works fine--make sure it measures in both oz. and grams. You should be able to pick one up at one of the big box office supply stores for about twenty to thirty bucks.
I got my postal scale from Staples for I think 25-30 bucks and it measures tenths of ounces up to five pounds as well as grams. The company that made it is called Pelouze (sp?) and the thing actually works!