Of course, it's not just the cost of airframes which needs to be considered...
Crew training - if the RN wants to use 100% RN crews, they'll need to develop a sustainable pilot and rear crew training system of their own. That's EFT, BFT and AFT/type conversion, plus ongoing recurrent training. For rear crew mission specialists, the training requirement would probably be even more expensive - you can 'buy' civil pilots and convert them, but you cannot do the same thing with mission crew.
Maintenance - unless the RN manages to join someone else's aircraft maintenance organisation, there's the cost of an approved type maintenance programme to consider.
Infrastructure - the RN will need a method of tasking, supporting and analysing all sensor products from whichever aircraft system they choose. Then the cost of disseminating the intelligence to the end-user.
Just a few issues. But good luck to the RN and I hope that they pull this off, no matter who flies and operates the aircraft. My gut feeling is that they are far more influential and creative than the oiks who run light blue these days, so have a pretty good chance of success...
