Christine, a good place to start looking is the "pink pages" of the GA News/Western Flyer. Quite a few airpark/airstrip properties listed,both in WA & elsewhere. Unfortunately, they all appear to be pretty spendy.
For example, right now there's a nice one listed: 38 acres with barn & 2600 sq ft mfd home on the Skagit River (north of Seattle), complete with it's own 1800' grass strip. I've overflown this one many times, it's real nice but IMHO not worth the $1.99M (yes,million!) the owner's asking.
This is one of the most extreme example's, there are others that seem to be more affordable but (again IMHO) ain't none of them much of a bargain. Might (might!) be cheaper to just buy land & build your own airstrip, but then you're dealing with other issues:zoning, permits,irate neighbors, etc.
FWIW land/airstrips in eastern WA & OR seem to be more affordable than western WA/OR, due to the law of supply & demand I guess. Hotter in the summer & colder/snowier in the winter, not to my tastes but some people seem to like it. The open country does kinda appeal to me though, around here you can't see the forest for the trees. Always thought that was just a goofy expression until I moved to western Washington.
Eric