Spending $$$ needed for Greece??

My husband and I are going to Greece from July 31st till August 11th and wondered how many Euros we will need. Our hotels include breakfast but we wanted to do some tours and have cash to use for lunches/dinners and the odd purchase from shops. Overall what is a realistic figure?

Also, if anyone has any "Must do" tours- would love to hear. (We love wine haha)

Itinerary is :

Athens- two nights

Paros - 4 nights

Santorini 4 nights