We had chartered out of Kos last year with the Moorings. Great base and great boat M494. They are very helpful and Andre, the base manager is a great person.
They check the vessel very carefully and have a diver go below the water
line to check for any damage; it's impoortant that you don't ground the boat. They also have additional insurance to cover the deductible, which I believe is $7000. US (that is the ductible without the extra rider.
Also try
www.sailonline.com for Mooring owners who may be selling their owners' time. It's about 50% off the moorings rates.