So what stopped the SAR from self deploying?
In practical terms because the crew will have been asleep in bed in the wee small hours, not watching TV. The MCA control room could have scrambled them if they had thought it necessary or if they had been asked - chances are neither happened because the MCA are maritime focussed (the clue is in the name) and that the Met police probably have had few dealings with the SAR flight at Lydd and barely know they exist let alone what capabilities they have.
As to costings - the new system may have changed but the only thing SAR billed the NHS for was hospital to hospital transfers - any rescue/medrescue that resulted in a casualty being taken to hospital was always free of charge.