The wizarding currency in the United States is the Dragot. Money in itself is thought to be one of the five exceptions to Gamp's Law of Elemental Transfiguration, meaning it cannot be created from nothing. Aside from the Philosopher's Stone which can convert other metals into gold there seems to be no other method of obtaining it. Attempting to duplicate money with the Geminio spell is also ineffective, as duplicates created from Geminio are worthless.