--You may get the same answers, but have you checked with vendors at other farmer's markets besides Pike Place?
--Any chance that any of the other members of the wedding party have some good flowers in their gardens and/or know someone in the business who could help out?
--Or does anyone connected with the wedding party own any property with lots of foliage? Evergreens like evergreen huckleberry, salal, and red cedar make lovely filler; if you can get some of that for free, you can get more bang for your buck with flowers that are nicely offset by the greens.
--Would it be unthinkable to use silk flowers? The higher quality ones are really hard to tell from the real thing without touching them, and might be available to rent or purchase at a lower cost than fresh flowers would be. Check with Display and Costume Supply and other display supply places for possible rentals.
--Also check with the Floral Design Institute (http://www.floraldesigninstitute.com/page001.00.00.htm); they might have leads on cheap sources of flowers and they might even be willing to sell you some of the work from their classes at a good price if the timing works out. I used to work in the same building with them and they frequently brought beautiful arrangements as gifts to nearby offices after their classes were over.