¡Olé! Cheap flights in October to Madrid and Barcelona, or perhaps one of the more underrated jewels in the Iberian crown, including La Coruña in the northwestern region of Galicia (in the local language, it’s actually spelled A Coruña). Most of these flights are on TAP Portugal and include an option for a free (!) layover in Lisbon, which is an amazing city worth a vacation all on its own. Don’t forget that you can always travel cheaply around Spain by rail, bus, or car share.
I also threw in a couple flights from Houston and Oakland, because why not.
Boston-Alicante: October 15-26 on TAP Portugal for $413
Boston-Barcelona: October 15-26 on TAP Portugal for $323
Boston-La Coruña: October 15-26 on TAP Portugal for $410
Boston-Madrid: October 15-26 on TAP Portugal for $323
Boston-Sevilla: October 15-26 on TAP Portugal for $412
Houston-Malaga: October 10-24 on Delta for $461
New York-Barcelona: October 15-27 on TAP Portugal for $419
New York-Bilbao: October 10-24 on Air France and Air Europa for $422
New York-Madrid: October 12-25 on TAP Portugal for $392
New York-Malaga: October 23-November 8 on TAP Portugal for $371
Oakland-Barcelona: October 11-22 on Delta for $459