American Airlines and Oneworld have Frankfurt and Munich, Germany on sale with Los Angeles LAX, San Francisco SFO and San Jose SJC ticket prices around $438 to $478 round trip.
Departure dates in $400s from mid-August to March 2018. Google Flights fare calendar shows prices over $1,000 for many of the low fare dates until you pick a departure date and see dates drop to $400s.
American Airlines San Jose SJC – Dallas DFW – Frankfurt FRA – DFW – SJC
British Airways San Francisco SFO – Philadelphia PHL – Munich MUC – Philadelphia PHL – San Francisco SFO
British Airways Los Angeles LAX – London LHR – Munich MUC – Philadelphia PHL – Los Angeles LAX