The Reg holds forth on the subject today at great length, extensive to the whole triforce imbecility.
Subsequent to my first post on this subject, I learned that the RN is buying newer model replacement Tomahawks at about £662,000 each. Hmmm. The price I gave was for the older, less capable model.
I think it's fair to use the sunk cost of the missiles actually employed, as presumably they would have been scrapped when the new ones arrived. Waste not, want not.