I myself would consider using PVC piping & connectors. It would definently be more cost effective and you could use blocks of wood for the weights. Depending on how you would want the wheels, you could again use pvc or even a hula hoop. Hope this helps.
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Carriage Frame by: Anonymous
I actually bought the template for the frame from one of the originators of the Frame. It cost $50 for the template and $300 to have it built. It then got stolen! So now I'm trying to find a way to build it in a more economical way.
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Frame for Cinderella Carriage by: Margit
I am afraid I can't help you with your question. The cinderella carriage is a pretty advanced design. You could try and contact the Event Decorating Academy. One of their courses includes balloon sculptures like the cinderella carriage.