No responses yet? Wow! Here's my two cents:
In my experience, London is usually the cheapest to get to from the east coast. London is, of course, a great city and if you've not been there - probably a good choice. Given the US dollars improvement of late, London is not a wickedly expensive as it was a couple of months ago.
Another option is Amsterdam. I've done a couple of long weekends there from the east coast. It's a easy trainride from the airport to the Central Station and from there you can get by tram anywhere in the city. There are plenty of options for lodging as well in all price categories.
There's my 2 cents!
