We've been hiring cars for our 2 week holidays for the last few years. With Olympic transfers being a nightmare, we were taking taxis. Add the cost of two airport to Plakias journeys and it's not a lot less than 2 week car hire. Having the car available makes it easy to pop up to Sellia for dinner, or nip up to Reythimno for a night out.
I usually book a few weeks before departure, and use either Holiday Autos or Rentalcars. Both are UK based, and have arrangements with various local firms so they can offer a selection and competitive prices. Last year we paid about £240 for a Golf - collected and returned to Heraklion Airport.
Prices do vary day to day, so it's worth watching the different sites.
I do check most years, but sadly I usually find that the UK sites are cheaper than using the local ones.
Having said that, if you don't intend leaving the resort, give Zak a ring for taxi transfers. Oh! - don't forget to let the reps know that you're making your own way to the resort, as otherwise they be looking for you at the airport and holding everyone else up.
