Check out www.economycarehire.com. I used them when renting in Ireland (same deal, very high deductible, no CC coverage) and their price was great compared to everyone else. Plus their rentals include a free additional driver and full insurance coverage. Their site is great because it spells out exactly what kind of deposits, fees, etc may be required. It's a British company, so you'll be charged in GBP, but it's worth a look.

I have no interest in this company, just a very happy customer.