I would agree with Tony and as it is for travel 2014 believe once the airlines launch schedules for 2014 you should get a better deal. Also think about other airlines (either do a search on Skyscanner) or try B.A and the tour operators whom also fly seat only into Athens.
a google search of the island Amorgos brings up an informative and interesting website the ferry crossing being 7.5 hrs from Piraeus, remember you will need to get from airport easy enough on one of the airport express buses to the port. This website gives all such information.
If you don't have it, it is
http://www.amorgos-island-mazagine.com but as far as flights I am sure you will get something a lot cheaper once flights are launched.