Delta Airlines has Frankfurt on sale for $404 round trip from Los Angeles, San Francisco and San Jose for travel departures from January 7 to March 19, 2019.
LAX or SFO to Munich is even lower at $391 round trip.
These are basic economy fares. Pay $90 more each way if you want a checked bag and seat selection at time of booking.
Delta Airlines San Jose SJC – Atlanta ATL – Frankfurt FRA – ATL – SJC
Delta Airlines Los Angeles LAX – Atlanta ATL – Munich MUC – ATL – LA