Via The Flight Deal, you can fly coach round-trip from lots of big (and small!) US cities like Seattle, Los Angeles, and New York, Portland, and Tucson, to cities in Europe, like Madrid, London, and Paris, for only ~$400+!
These deals are good for flights on airlines like Delta, American Airlines, KLM, Air France, United Airlines, and more!
I found a flight from Los Angeles to London departing November 11, 2017, and returning November 20, 2017, for ~$459.
And a flight leaving Phoenix on January 17, 2018, and returning from Madrid on January 31, 2018, for ~$385!
There are cheap fares available on various routes through February 2018.
Fly From the US to Madrid for Only ~$400!
Here are the details. And how to search for deals from your city!