Sailor Moon Store in Shinjuku Isetan.
The cheapest clothing there is the $80 t-shirts, the dresses, tops and skirts are all between $100-$200. The dress on the Princess Serenity mannequin is over $1000, and I couldn’t find any price on the other white dress. They were also selling manga kanzenban and iPhone5 cases
One of the staff there spoke to me in quite passable English.