In reply to GarethSL:
all of the budget rentals in spain are supposed to be nightmares. They obviously don't make their money on renting out cars for 1-2 euros a day. You either buy the insurance or they try to stiff you when you bring the car back.
I rented 3 times when I was in spain last, one from recordGo, Goldcar, and Dickmanns. Just read the relatively short term agreement to make sure you wont get stiffed on fuel and mileage and then take a video of the car so you can go back to it for any damages you might have missed when the checker comes and tries to bill you for damage you didn't cause.
I personally didn't take any insurance out because I'm american and a lot of our credit cards have rental car insurance as a benefit. RecordGo and Goldcar were great(didn't even try f*cking me over when i returned the car), they just put a pending charge on the credit card and you get it removed a week or so after returning the car. Dickmann's on the other hand I would recommend against because they actually charged my card 900 euros and I had to email and call them constantly over the span of 3 months before they finally reimbursed me(which to their credit they gave me all of my deposit back).
tl;dr: budget car rentals are predatory in spain but as long as you do your reading on the policy and make sure you document all the damage(even the smallest scuffs), you shouldn't have any issues. If you want piece of mind, pay for it with their insurance or a non-budget agency.
Post edited at 20:42