KLM has San Francisco to Dublin on sale for $479 round trip for departures from mid-September to early May 2019. I am finding low fare itineraries only when including a KLM long-haul flight SFO-AMS or AMS-SFO combined with a Delta domestic connections via New York or Atlanta in one direction.
Google Flights shows low fares with Delta and Air France too, and many itienrary options, but I have only been able to price sub-$500 tickets through KLM with a long-haul KLM flight in one direction. Delta and Air France price in mid-$700s and all Delta flights price high too on KLM.
These fares are not matched by Oneworld or Star Alliance.
KLM San Francisco SFO – Amsterdam AMS – Dublin DUB – Atlanta ATL – SFO
KLM San Francisco SFO – New York JFK – Dublin DUB – Amsterdam AMS – SFO