I suggest that they quickly apply for a credit card that offers a Zero% loading and transfer fees for use in Europe. Which? recommends Saga (only available to over 50's like me), Halifax Clarity, Nationwide, Post Office, and Sainsbury's.
Check out the Which? web pages as using a Debit card overseas can be very expensive, and if a Car Hire company does take a debit card, then they are also likely to be more expensive.
The cards generally offer a far better exchange rate than cash, and paying then off in their interest free period will ensure the best overall deal.
Also have a look through the numerous comments about car hire in Spain before choosing a deal!
Mike.
This message was last edited by MikeandHelen on 13/08/2012.