The absolute cheapest prices are to the East Coast, where Philadelphia, NYC, and Boston can be reached for only €3019. Most of the Midwest can be reached for only €3300 while the West Coast gets a bit more pricier at €5000.
The nice part of the fare sale is that the prices are valid for travel on Lufthansa or SWISS, however your travel needs to originate in Germany. You can also find these fares for travel on United flights from Germany as well.
The fare sale is in place until May 29 and is valid for travel between June 30 and September 10, 2017.