Another option to keep the costs down in a restaurant is to consider finding a restaurant that has large gift certificates on restaurants.com and going that rout. Some of the restaurants offer certificates for $100.00 off of a $200.00 purchase and if you buy them on sale (they are 80% off right now with the promo code GIVE) you can eliminate the venue fee and really bring down the costs of food.
I quickly tried searching the Tacoma area for a restaurant that offers a $100.00 certificate and could not find one, but there are several in the Seattle and the South King County area if that is an option.