Another suggestion based on current promo sale of Star Alliance airlines are round trip flights from Europe to Seattle. Fly with Lufthansa / Air Canada from Rome, Amsterdam or Paris to the largest city of Pacific Northwest territory already for €310. This is fare for a return flight including all taxes and checked luggage.
If interested in this promo deal with Lufthansa / Air Canada you can find the lowest farest to Seattle in travel period till 22nd of June. Max stay 3 months. Book by 12th of February 2016.
Before you book. Some of the flights may require airport change in Paris or London. You may find flights without need of airport change for just slightly higher fare so choose properly your routing.
Travel dates.: Vary by each origin. The easiest way is to use service of Ebookers as they offer +- 3 days searching view. You may then compare the lowest option and use your preferred booking agent.
To check our your connection possibilities to above cities from your home town we recommend to use service of Skyscanner. To book cheap accommodation in US you may use server Venere or Hotels.com. They are now also offering 8% discount code. If interested please check here.
Booking sample of cheap return flights from Europe to Seattle from €310! In this case you would be departing from Rome to USA on 14th of May and returning back from North America back to Italy on 29th of May 2016.