British Airways currently offers various interesting routes how to get to North America with very low budget. Another solution you may consider to book if you want to travel USA are an open-jaw flights on route Stockholm/Oslo to New York with return flights from Detroit back to various airports in UK or to Germany. Such an open-jaw ticket is possible to purchase from £218!
For a bit higher but still very attractive rate you can consider to depart from Copenhagen or Warsaw.
Travel period: from November 2015 to April 2015!