Costs of long running programs of any type of military hardware are always complex and it's hard for any two people to agree. The US sometimes doesn't include all the items in the cost of a piece of kit, you have the question of how do you handle inflation, what is your base line, do you include spares? training? Things like the missiles and torpedoes?? Decommissioning costs?? Bases?
I'm not sure either that you can compare apples and oranges so easily - yes, you can compare say an F-35A with an F-35B on costs and performance with reasonable accuracy but an SSN against an SSK? Very different animals, and would be deployed very differently - and have a very different effect on the strategy you'd adopt.