You could also take a ferry to Naxos or Paros en switch ferry there.
More info on dates etc. at the site www.openseas.gr
Blue star ferries have connections on these lines, you can check their homepage too.
You mentioned no dates, so I can't make out if you would get there faster by ferry or by airways.
Try http://www.gtp.gr/. I use this every year to plan my trips between islands. it's very reliable.
This is helpful - thanks very much
I forgot to add; if you stay in Livadi on Astypalea try Anixi Studios. The rooms are clean and modest and overlook a garden full of orange and lemon trees and it's only five mins away from the nearest beach. The owners are lovely people. I'm planning to go back in September ( tel +30 22430 61269 or 61460). Or you may see the owner , Nik, in the port when you arrive.
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