After narrowing it down to several choices (which I sadly can't share because they're no longer available), this is the one I picked, for $98:

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It has a similar cut to the bodice as the bridesmaid dresses, especially with the twisted straps, and I love the little pleats on the skirt!
And check out these hot Chinese Laundry heels I got to go with it, for only $35 from Endless.com! Miss Cheeseburger looked at these as well in her search for purple wedding shoes.
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The multiple straps on the heels go nicely with the waist detail on the dress, and they're the perfect shade of purple too!
How far in advance did you pick out your other wedding event outfits?