I had an interesting car rental experience last year. I booked on line to rent a car from Dollar at the Granada airport. The fee was listed around 100 euros for the week with some added taxes. I called Dollar in the US, but they couldn't tell me what the exact amount of those extra fees would be. I asked, "It won't be 300 euros?" and they assured me that the price would not be that high. I arrived at the Granada airport and eventually found Dollar, who had changed their name in the mean time. Despite calling my credit card company in advance regarding my trip to Spain, my credit card would not work for the car. The receptionist offered to let me pay in cash. The fee? Three hundred euros. I ended up taking the bus and walking. For me, it was fine. I was glad not to have had a car in the mountains anyway. It sounds like Admiral has the right idea and by paying in advance, you will know the exact amount of the car rental.
Have a good trip, Admiral44