American Airlines, Delta, Iberia, British Airways and various other airlines have round-trip flights from Austin or San Antonio (AUS/SAT) to Madrid or Barcelona (MAD/BCN) for $507-$512 with a connection. Flights July to August. 7-day minimum stay required.
Other smaller cities in Spain may also be available in these months, but may have longer connection times or multiple connections.
As of June 07th. Spain is reopen to fully vaccinated U.S. Citizens. Must register on the Spanish Health Website.