Budgeting for Greece is always going to be subject to what your expectations and needs are. Assuming that you, like many travellers, like to eat a filling breakfast, savour maybe a light lunch and feast on a heavier dinner (or vice versa), enjoy a drink with your meals and are not totally vegetarian/vegan and prefer to sleep in comfort and cleanliness, then there is a set of figures that can be guesstimated.
Of the above groups the Dodecanese probably constitute the best opportunity to mix islands between groups. You could, for example, take the Blue Star Ferries and map an island-hopping route that essentially heads in the same direction. In this way you could take in some of the Cyclades – Syros, Mykonos, Patmos, Naxos and some of the Dodecanese – Patmos, Leros, Kos, Chalki, and Rhodes – without any backtracking. Hellenic Seaways is another major ferry company whose routes you may want to explore.
Since St. John is part of the U.S. Virgin Islands, U.S. citizens can visit without a passport. There are quite a few bargains on both St. Thomas and St. John right now, so it’s a good choice for travelers on a budget. Snorkelers should not miss visiting Trunk Bay, one of the best snorkeling spots in all of the Caribbean for seeing amazing marine life.