revisit Pacificplex.com today, but found that they have a larger selection of dresses on amazon right now. In fact, there are a bunch of dresses that could easily be used as bridesmaids dresses since they are available in multiple sizes, sometimes even up to 5x. AND most of the prices fall below $100. I can't vouch for the quality, but I'm pretty sure they'll last through the wedding day (or prom). I also saw a few dresses that could be used for the bride.
Most of the dresses that were vintage inspired were in 30s-50s styles, and some had multiple colors. The dress pictured in this post is available in 10 different colors (including ivory and white) and is $69.99.