DDO- Doubled Die Obverse (the side with the President, Queen, King, Dictator....) DDR- Doubled Die Reverse (the other side) Doubled Die- Is a Die that was struck twice which in return produces coins with a doubled image. If a coin is struck twice, that is a completely different animal.. a double struck coin.
It depends on how much of it was double struck. Check out ebay. You'll see quite a range of prices depending on the strike.