I live in Auburn, right up the road from you
I really can't advise you as to where to purchase the actual decorating supplies, as I am just a hobby baker.
BUT as far as the baking supplies go, have you checked out Cash and Carry? You can save a ton of money at that store, if you are willing to buy in large quantities. I get my eggs, flour, butter, sleeve fillings, puddings, HR shortening, Bettercreme, as well as a multitude of other goodies we bakers need.
I go to the one in Federal Way....I am sure that they have locations in Tacoma as well. The prices are as good as Costco, but with NO membership fees.