I'm in Kent, so I don't know of any real shopping suggestions. I do my flour shopping at a little HFS in Burien called the grainery. They will mill the flour for you from the bulk bins of ingredients. I just bought 4# of garbanzo beans, 2# of tapioca, 1# of buckwheat, and 1# of potato starch, all milled into flour for less than $20. Such an awesome deal. My idea would be to shop there, but make it a once a month thing. Get some storage tips for larger amounts of flour and buy 20lbs of each of your staples at a time. Maybe use a deep freeze for storage.
I'm only cooking gf for myself and my 20month old, so flour lasts a LONG time here.