One more vote for Basimakopoulos.  My boat was on the hard there for the winter 2017/18.  The yard and their contractors do excellent work and prices are reasonable.  They will connect you with a very reasonable one way car rental from/to the Athens airport - about a 3 hour drive as I recall but scenic.  Joerg Esdorn, A55 #53, Kincsem, Almerimar, Spain