we are not replacing the SARF because it costs a lot (and like everyone else you assume it is more expensive without any figures to prove it) we are replacing a military SARF with a hybrid because the MoD has failed to invest in medium lift helicopters for the last 20 years and the ones we are using now are getting old and tired.
Would it be unfair to suggest that an equally (more?) valid reason was that it was finally accepted that UK SAR is not 'core' business for the
armed forces who are mighty stretched at the moment; and that rest tours and transferring additional skills back to the front-line notwithstanding (both of which might be moot points for the existing RAF setup) there are better things for the MOD to do with their assets (which includes the aircrew).
To paraphrase a flag rank some time ago
"I'm struggling for a/c and crews in 'stan, so why on earth would I want to have NVG trained, Mountain experienced crews sitiing on their a***'s in the UK"
Priorities !