Most auto insurance companies in America don't cover you outside the US/Canada, however some credit cards do cover you in some countries, including Spain. So check with your credit card companies and see IF, and above all, WHAT they would cover in case of accident.
Assuming none of your credit cards cover you, or assuming you don't want to go through the trouble of filing a reimbursement claim with your credit card in case of accident, there is the option of buying insurance with no insurance excess (no deductible).
I generally choose the latter option, since a friend had to file a claim with the credit card for reimbursement, and it was a bit of a hassle for him, even though it wasn't a large claim, so I can only imagine how it would be in case of major accident. Also consider that the credit card would REIMBURSE you, however you would need to pay for the damage upfront, and then claim reimbursement with the credit card once your return home.
I generally use a consolidator, using the two websites below (they are actually part of the same company based in Maine):
www.autoeurope.com
www.kemwel.com
Their contracts, if you so choose, come with full no deductible insurance (no insurance excess) with the rental car company.
I tested a sample week in September 2015 with both websites and i could find an economy car for approximately US$200 per week, with full NO DEDUCTIBLE insurance. The best price for the week I tested was with Hertz, however you might get different results if you select different dates.
Give it a try. I don't think $200 is that bad. Last month I spent $457 for 16 days in Italy using the above, therefore it seems more or less on the ball park I paid. It's also not much more than I would pay in the US.
