I've been looking up airfares for this summer (well, later this summer and in to autumn, depending on how you look at it) and I think I've managed to find all three flights for less than $1,300 total- which, considering how late in the game it is- I am quite pleased with.
In any case, these are the dates that I'm looking at, just to give you a heads up for when I'll be in your area
London to New York: Thursday August 14
New York to Seattle: Saturday August 30
Seattle to London: September 12
So, not quite two full weeks in Seattle which is really too bad-but! I will be back for Christmas this year.