Via SecretFlying and Mommy Points, you can fly coach round-trip from a number of big (and small!) US cities like Seattle, Los Angeles, and New York, to cities in Europe, like Madrid, London, and Paris, for only ~$400+!
And via The Points Guy, you can fly round-trip from New York (JFK) to Los Angeles and San Francisco for only ~$216+!
These deals are good for flights on airlines like Delta, American Airlines, United Airlines, JetBlue, Virgin America, and more!
I found flights from Seattle to Madrid for ~$406 leaving February 3, 2017, and returning February 11, 2017.
And a flight leaving New York (JFK) on January 14, 2017, and returning from San Francisco on January 21, 2017, for ~$267!
There are cheap fares available on various routes through May 2017.
Fly From the US to Madrid for Only ~$400!
Here are the details. And how to search for deals from your city!