Is this a bridezilla thing to do?

I picked my bridesmaids dresses a while back. I chose an inexpensive OTR dress from JC Penneey. My girls have all bought the dress I picked. They bought at different times so 2 of them paid $75 but 2 of them only paid $30. Anyway, looking at the dresses now I dont think they fit the formality of my wedding and I want to go with something more traditional and formal. Would it be a bitchy bridezilla move to ask them to get new dresses?? What if I offered to pay for the new dresses?