A good deal to London from Portland, Oregon PDX is a $610 round trip ticket on American Airlines for short season departures Oct 30 to December 15, 2016. There are some lower fares down to $578, but those lower fares tend to have an overnight or change of airport and some exceptionally long nearly-30-hours itineraries to get home from Europe.
Keep it simple.
American Airlines Portland PDX – Dallas DFW – London LHR – Charlotte CLT – Portland PDX
Here is one of the lower fare overnight itineraries that will add a lot more than it saves in overnight expenses if you need a hotel.
Outbound: Portland PDX – Phoenix PHX – New York JFK – London Gatwick LGW
Inbound: London Gatwick LGW – New York JFK (overnight 7:50pm – 6:45am) – Phoenix PHX – Portland PDX.
Unless you have friends or family who will stay up all night with you, that is a horrible itinerary for a hotel night with probably only time for about 4 to 5 hours sleep and New York is not cheap for hotels.
Now if you have friends & family in New York, well then, in the past year half of my family reunions have been three or four hour gatherings when someone comes and picks me up at some airport, often late at night as I am passing through a city on my way to or from Europe and a short overnight layover.
Fortunately for me and them, my family has always been kind of 24 hour people.