What about eastern Oregon, like La Grande? I've only been through it once, but it seemed like a nice place... and according to city data, the weather sounds like what you're looking for:
//pics.city-data.com/w1/lha18024.png (broken link)
//pics.city-data.com/w2/hum18024.png (broken link)
Also, like someone else suggested, parts of southern Oregon might work. Ashland is a beautiful town, which is quite dry compared to most of western OR... but in terms of cost, it's fairly expensive for the state. Northern California has lots of low-humidity spots, basically anywhere along the valley or coast. The coastal towns like Eureka/Arcata have very mild weather, where it's never really hot or cold. But the trade-off is constant gloom, where you don't see the sun for weeks at a time. It's also pretty rainy, but is rarely humid when the sky clears... perfect for my taste!

The Central Valley is very dry, though temperatures can really soar in the summer. I lived in Stockton for a few years, and
frequently saw temps. above 100 degrees. Yuk!