If you only spend 3 Months in Spain every Year.... Don't Buy....Rent

The Agencia Estatal de Administración Tributaria, AEAT will judge if you have any capital gains tax to pay based on their own estimates of valuations irrespective of what evidence and documents you have.

In my experience (based on 18 years of coming to Spain for about 12/13 weeks a year mostly off season):

1. It is generally cheaper to buy than rent. The cut off point is under 3 months off season. If you use it in season owning wins hands down. But the convenience of having your own furniture and clothing available at any time and knowing that it will be habitable when you get there outweighs a lot of the financial consideration.
2. The running costs of a permanent flat in Spain are less than half of a site/mobile house in the UK. And over the long term you make a capital gain rather than a loss.
3. Generally if you are staying more than a month off season and you make an offer based on the long term rent  it is accepted.
4. Second hand cars are very expensive at the moment and have always been a little higher than in the UK but the situation at the moment is ridiculous. I came out this year thinking of updating my old Nissan only to find similar one with higher mileage available for more than I paid 8 years ago!
5. Renting a car is sometimes cheap, but not at the moment. It only takes arriving in Spain once at Easter and being let down by a hire firm to convince you that owning is better. (Likewise it only takes one shunt to convince you that paying the extra insurance scam is worthwhile if you do rent a car).
6. Renting property is to be advised if you have yet to decide what part of Spain you want to be in.
7. When you make the comparison between renting and buying you now have to take into account the extra £40 per flight it is going to cost you when you are forced to pay for your hand baggage (an owner has all the clothing needed in Spain).
8. Sharing a property with good friends or family can make the outlay low and the on-costs cheap especially if you wish to be here at differing times.