The rules are complicated... largely due to recently re-issued JSP360 regulations. I think I am right in saying the £150 ('ish) quoted above is a flat fee for regular users If you plan on less than a dozen movements a year, the insurance fee is much less... (but of course, every landing, take-off or approach counts as a movement... so don't plan to pound the visual circuit!).
Best advise, before giving up the ghost, is as many have said above is speak to Ops at the base you intend visiting... they should be a. able to sort out the necessary PPR and b. advise on cost