Here's some rough budget costs over 5 years:
Half decent car (Starts everytime you go over) £3000
Tax MOT Insurance servicing costs unexpected repairs £1000
Total (Minimal repairs / expenditure) £4000
Hire car (Class B, 4 door, aircon, 5 seats, NEW, CDW)for 5.71 weeks per year
Total (Peace of mind)£4000
The decision is based on two factors, one amaount of time you spend over there (fixed) and two predicted cost of repairs to purchased car (variable).
I know why you have thought of purchasing, as I have to. It's a notion, but not necessarily a practical one. I always hire. There is another cost and that is the transfer from the airport. If you hire from there you will have no transfer costs (petrol only).
Steve