I live in one of the northernmost neighborhoods in NE Seattle. I have been tracking housing listings for the last several months, as we will be buying sometime in the next year. Housing costs depend very much on microlocation. You can probably still get a 3-4 br home in my immediate neighborhood (I live on a major street) for 500-700k. But if you go east a few blocks, over the crest of the hill where you start getting amazing views of Lake Washington and the Cascades, prices jump to 800k-1mill+. That being said, I have noticed a few listings in that neighborhood where they have listed high and now are dropping the list price.
Lake Forest Park is nice, especially the Sheridan Heights/Sheridan Beach (if you have $$$) area. Sheridan Beach is on the Burke Gilman Trail, which gives you a straight shot by bike to the UW.
Shoreline housing (anything north of 145th) is typically $100-200k cheaper than similar units in the Seattle City limits. Not sure why that is, as Shoreline schools are generally considered better than Seattle schools.
Issaquah/Sammamish is very congested, and not that much cheaper than Bellevue/Redmond.
Carnation/Duvall/Fall City are not that cheap anymore, either, and you have to drive long distances to get to shopping, drs. etc.