Cheapest way to travel from Greek islands to Milan?

Hi everyone, just helping out a friend with her families holiday trip plans.
I can't seem to find any good deals for getting from preferably Santorini/thira back to Milan for their flights home.
They are flying from Naples to mykonos on 29th august staying for about 3 days in mykonos then a ferry to Santorini and staying for about 3 days there.
So the problem is getting back to Milan for the flight home.(4th or 5th sept)
Don't know if its best to get the ferry and fly from mykonos (backtracking-meh) or fly straight from thira but flights are like $270.

So all you pro ozbargainers, help me find some secret cheap flights/routes

Thanks!