I'm in Eastern Washington, and Anchor is in Minneapolis, so roughly the same distance to either of us, I would think. I went through the process of registering (I hate that,too! zip code should be enough to calculate shipping) just to find out shipping. One box of 250 was $9.88 cheapest. Four boxes was $13.34. That should give you an idea, I think. It comes to about 5.5 cents each. Not a bad price.
ETA: Meant to say, 5.5 cents in the 4-box price. Obviously the more you buy, the cheaper the per envelope price.