Belle from Beauty and the Beast costume?

I would like to be Belle from Beauty and the Beast for a halloween program. Where can I find a pretty dress, with affordability in mind? It can be either prom dress or real costume, I will be using it until it doesn't fit anymore, due to voulenteering every year.|||http://www.ubrides.com/home.php?cat=523%26amp;鈥?/a>