United Airlines has a special nonstop flight flying San Francisco to Barcelona on February 27 for Mobile World Congress 2019. The deal is United has this flight on sale for $205-$220 for Basic Economy one way from most airports in California. Checked bag ($60) and self-selected seat $30 extra.
This deal only works one way due to prohibitively expensive return flight prices with United.
United Airlines San Francisco SFO – Barcelona BCN nonstop
From my home town of Monterey and many other airports around California, there is a same-day Wednesday February 27 ticket price of $209.20.
United Airlines San Francisco SFO – San Luis Obispo SBP – Barcelona BCN nonstop
I see these $209 fares from airports as far away as San Diego SAN and Arcata ACV.
You can fly to SFO on Tue Feb 26 and fly Feb 27 for around $220 per ticket.