I am using fresh white hydrangeas in mint julep vases as centerpieces. I got a great price on them $1.50/stem and I won't need many b/c they are bulky. I will also be able to assemble centerpieces 2 days prior so I don't have to worry about last minute flower chaos!
If you live in the lower mainland try the growers for the flower auction; that's where I found mine.
http://www.ufgca.com/homepage/subpages/link-grower.html
If you like this centerpiece idea or if you just want to save some $$ on decor check out my post on sharing decorations in the shopping- buy/sell section of this site.