Yakima Valley

Barnard Griffin and Snoqualmine come to mind. Both are fairly priced and pretty good quality for the price.

Try not to be put off by the distance to WW. At least try to make it to the Prosser (and from there to the Red Mountain) area. If you really can't make it there try visiting the Woodinville (suburb of Seattle) area. A lot of WW and other top notch wineries have established tasting rooms there. You won't see any vineyards there but you can taste a lot of good wines within a few miles of each other.

Woodinville is close to Snohomish where we'll be. I may have talked them into making the drive to Walla Walla but still may go to Yakima as well.

If you're going to be staying in Snohomish, then by all means visit Woodinville. If you travel to WW, you'll be going through the Yakima Valley. Although there are many good wineries in the YV, they are pretty spread out. The nice thing about WW is that there are so many so close to each other.