A chap called "Blas" at the local Ford dealer will make it as easy as possible.
If you want to take a car from the UK, the trip is 1350 miles or so from Calais and 650 or so from Santander/Bilbao. The roads are pretty decent, tolls will cost under 50 all the way from Calais and the mountainous bits are pretty spectacular.
Formula 1 hotels (Formule 1) are pretty cheap at about 25 euro per night - they have a website and you can book in advance. Ibis hotels are part of the same group and are slightly more expensive. "Hotels" with lots of neon lighting, by the way, are brothels!
Itīs a comfortable 2 day trip from Bilbao or you can push it and do it all in one go (about 13 hours driving). Obviously double that from Calais.
Insurance for UK reg cars can be had from a number of cources and these folks are good to ceal with
http://www.seviour-insurance.com/
Petrol in Spain is cheaper than the UK and diesel cheaper still. LPG is very hard to find. In France, unleaded is about the same as the UK but diesel cheaper.
You can just about live without aircon, but I would not recommend it. UK reg LHD cars can be cheap on ebay and autotrader/exchage and mart.