You need about $600 in cash for food, incidentals, and souvenirs. Many places you can pay by card. The national currency is the U.S. dollar!
The cost of a "typical" dinner: 20-30 USD in a good restaurant. Tips: 10% of the order.
Bring cash to Galapagos! ATMs may not work, connection of payment terminals may be slow, to pay by card may add up to 4% commission.