There will certainly be a cost involved, which is why there will be an optimisation first, before the full monty. The Mk3s will all need an MLU soon, so that's an opportunity for the RN getting a good amount of the work done.
They would never have been asked such a question as the ac does not presently have a clearance to operate from a ship.
why does not having a clearance stop someone from asking a question? It will have, so the question is relevant.