On TAP Portugal you can fly from Boston, New York, and Miami to many European cities for about $250 roundtrip! On flights have a layover in Lisbon and then continue onto your desired European city. Some cities are more expensive then others, but it looks like everything is less then $300. Some cities include: London, Oslo, Brussels, Paris, Madrid, Barcelona, Amsterdam, Zurich, Rome, Milan, Geneva, Copenhagen, and Prague. And of course you can just fly to Lisbon which is an extremely quick flight from the East Coast.
You can book on Orbitz or Priceline and your ticket is refundable until tomorrow evening. So you might as well book now, and think about it later! You can check out the SecretFlying post to see all dates they found with this eligible fare.
Since this is most likely a mistake fare, there is no guarantee that they will honor this fare, so just keep that in mind when making hotel reservations, etc.