Repairing a shattered base on antique statue?

I purchased this antique religious statue online and when I recieved it, the base was crumbled. It was originally in a church. It measures 31/2 ft tall and 4ft wide. It has four figures, including Jesus that are all standing on the solid plaster base. Only the base is damaged. The figures are still whole. It seems that I will have to somehow build a mold to sit the statue into with wet plaster. Any ideas how to take on this project? Any help will be appreciated.