As I understand it by now all the Legacy Hornets should have been retired and replaced by F35Cs, at whatever low cost they were promised at with the low maintenance costs promised.
Unfortunately as the F35C has yet to gain IOC, plans have had to be made to increase the lifetime hours of the Legacy Fleet from 6,000 to 10,000. At a wild guess I would have thought that this was rather an expensive structural regeneration exercise.
What is being done to the avionics of the Legacy Fleet to bring them up to date is of course another matter, that no doubt could cost a fair sum. Without an upgrade to the avionics are the Legacy Hornets effective weapons systems in contested airspace?
By now the USMC was I would have thought planning to have a fleet of F35Bs and Cs as the backbone of its fixed wing attack fleet unfortunately it now has rather old and expensive to maintain fleets of Legacy Hornets and Harriers.