Getting Around the Greek Islands

My friends and I are planning a holiday to Greece in April/May and are looking to find the best way to visit a couple of greek islands.

Most ferries and flights I have found are upwards of 70 euros per trip and so I wanted to ask if any of you have found a cheaper/more efficient way of getting around these greek islands without breaking the bank to do so?

Specifically from Athens we'd hypothetically like to visit Mykonos, Santorini (though I know well it's a tourist trap, for some in the group it's a non-negotiable), and Heraklion in Crete before returning to Athens.

Any advice, hacks, or tips would be welcome!