Buy a flight only to Athens, get the ferry from Pireaus to one of the islands, and get somewhere to stay when you get there. Still works in most of them.
If you want to stay in a family-run hotel, rather than a place that is part of a chain, or a big company, it can be even cheaper, if - having discovered the best deal available on-line for a room - you then phone up the hotel direct and make a booking with the proprietor.Don't use a holiday firm. 'Build' your own holiday using t'internet. You will be amazed how much cheaper it can be.
try teletext holidays online.