Flights

In order to get to Santorini the cheapest and fastest way possible, we suggest booking a flight to Athens, then a separate flight to Santorini. 

There are non-stop options to Athens, Greece from Newark, John F. Kennedy, and Philadelphia Airports. These range from $500 and up. 

Round trip flights from Athens to Santorini can easily be found for around $50. Use Skyscanner to find this flight as well. 

I would suggest creating a "Flight Price Alert" for the days you plan to arrive and depart through Skyscanner or Hopper in order to get alerts for the cheapest flights. 

Other Flight Options

If you want to start your trip somewhere in London before coming to Greece, you can fly to London for approx. $400 round trip and then fly from London straight to Santorini for another $200 or less.... set flight hopper notifications for these flights as well.