American Airlines have put Atlanta, Detroit, Minneapolis or Cincinnati to many Spanish cities on sale.
For example, fly from Atlanta to Ibiza, Spain for only $396 roundtrip (see image below).
Ibiza/Palma de Mallorca/Barcelona/Bilbao/Valencia/Alicante, Spain
Availability from August to November 2017
Allow the search to complete, then click an OTA to view the advertised price: