I know this is too late for you Stella but maybe it helps others.
The other option is to book a car over the internet using one of the companys which find the cheapest offers around from the major car hire companys. I took my family to Plakias in May and we got a group D car (Peugeot 307, Opel Astra) for 400 Euros for 2 weeks everything included through Sixt. You can pick up and drop back at the airport so no transfer hassles. We used
http://www.FASTCarhire.co.uk but it is always best to compare proces and shop around. They provided a very good service but as ususal with Car Hire Companys be very careful to check every detail of the booking. I have to hire cars quite frequently and I have lost count of the number of times I have been asked to pay extra for something that has been pre-paid, the most common being child seats.
Of course it is always good to support the local businesses and it may be possible to get a better deal after you arrive. Pay your money and take your choice !
Good luck and hope you are having a great holiday.