Mold to make sculpture trophies

This sculpture will be flat and square on the back. The front will have a raised look to it. I would like to be able to pour plaster or something inexpensive but semi durable into it. see attached photo for an idea. It would stand up on its own. The dimensions would be something close to 10 inches high and 8 inches wide the middle up to the top would be 1 inch thick. The bottom half would be 2 inches thick to help the block stand up. Their would be a smooth spot in the front bottom, maybe 5 inches long & 1 inch high for engraving or a label. The finished product will look like a tombstone standing up with a raised figure on the front