American Airlines and Oneworld Alliance have San Francisco to Munich priced from $365 to $390 for departures from late March to early May. Lowest priced flights are American Airlines operated flights connecting domestically. There are several itineraries I saw with a 20-hour overnight layover in Charlotte if that is to your liking.
I particularly like the British Airways and Finnair flights directly from SFO to Europe. Booking a long transit overnight in Helsinki is an easy option to find on some dates.
$386.23 round trip  Airlines ticket for British Airways and Finnair operated flights
Monday April 1 – British Airways outbound: San Francisco SFO – London LHR – Munich MUC
Tuesday April 9 – Finnair inbound: Munich MUC – Helsinki HEL (overnight layover 22:15pm-16:20) Wednesday April 10 – Helsinki – SFO
These itineraries can be booked through American, British Airways or Finnair. Google Flights seems to only have deep links to AA tickets. Good to check BA and Finnair sites for different itinerary options. I found ticket pricing in $360s on Finnair.
