Until we sign a contract for the aircraft, we won't know the price. I suggest that we don't need to sign a contract for another eighteen months, perhaps more if we go for a shorter trials and IFTU period, although that has risk of its own, or delay the IOC.
There are people talking here as if "the capability" all has to come in a one'r and exactly when the EP plan specified, otherwise the whole thing is not worth having. This is a fifty-year capability we're talking about, so that sort of assumption is just b0ll0cks. I'm not suggesting for one minute that it is allowed to drift, but the facts of the matter are that the aircraft developmental trials are proceeding (not without issues, but par for the course), the EMALS programme looks good (albeit with some UK specific risks, though not those the window-lickers in the PAC thought they'd found) and the shipbuild is looking very good at the minute.
Whether the first ship is ready in 2019 with the IOC F35, or whether a lease FA18 deal is done, or whether the IOC is delayed is somewhat irrelevant at this point. Given the unknowns, which are being worked on, time to stop speculating and let the real engineering (as opposed to financial spreadsheet engineering) firm up.