Do not ask for more money. It would seem (or be, depending on your perspective) extortionate, since you'd essentially be holding the solution hostage that you a

Do not ask for more money. It would seem (or be, depending on your perspective) extortionate, since you'd essentially be holding the solution hostage that you agreed to build for a more or less agreed upon price. Instead I would ask for a performance bonus or something, perhaps contingent upon your ability to deliver it quickly, among other things.