I am not aware of the claimed savings being offered between the P68R and the 135 as such information was apparently among the redacted sections of the documents I have seen. The usual claims made for fixed wing are that they might be one third of the price but there are so many variables. One saving of course is thay are two crew rather than three. No room for a third.
Most of the other questions lie in the how long is a peice of string category, difficult to quantify.
The ball park cost of a pre-NPAS unit was £1M per aircraft per year flying around 1,000 hours annually. So a 10,000 hour airframe might be first cost + £1M x10. That is much too simplistic.
As the older airframes, including G-YPOL, have already demonstrated 12,000 hours is no real problem and North Sea helicopters have flown way more than that so there might be time enough with the remanufactured airframes as long as none of them turn out to include the [inevitable?] rogue.