When we were in Plakias we went to every car hire place and the prices were all expensive compared to quotes given online. The cheapest we found was 156 Euros for a week, class A. Not being happy about this we went online and found Imperial car hire who claimed to be in Damnoni, for 98 Euros per week, and they would deliver the car to our rooms as well. We booked with them, and on the day of delivery they phoned and said they were busy but the car was waiting for us at Monza car hire, next to the Lamon hotel. We walked along and picked up the car and everything was fine. I'm not sure how this works, as Monza quoted me 156 in person, but then another company online using the same people can give you the same car for 30% less. Seems like a bit of a tourist trap if you just turn up.