There are low fares to central Europe with a variety of airlines. Some of the lowest fares from Bay Area airports are Budapest, Hungary and Prague, Czech Republic at $350 to $375 round trip using AARP $65 off discount link. Many other cities in Poland and Germany are priced around $410 round trip.
Low fares in this fare war are mostly only September and October dates.
AARP membership is $12 and there is no age restriction.
British Airways $367.25 round trip
San Francisco SFO – London LHR – Prague PRG – LHR – SFO
Tue Oct 3 – Tue Oct 17
British Airways $379.90 round trip
San Jose SJC – London LHR – Budapest BUD – LHR – SJC
Tue Oct 3 – Friday Oct 13
British Airways $379.90 open jaw Budapest and Prague
Tue Oct 3 San Jose SJC – London LHR – Budapest BUD
Tue Oct 17 Prague PRG – LHR – SJC
Oakland OAK has fares as low as $350, however, OAK-LGW route means transferring to LHR for most continuation flights to Central Europe.