The Mini Reliefs
These are a series of lowest priced  wall mounted relief pieces.  They are all available in all all three mediums- bronze, alloy and black, excepting for the alien.  They come with a hole drilled in the back.  The way these pieces are produced so economically is t hat they are made by using the left overs from the main casting process. 

Foot has provided an explanation of the cold cast bronze and cast marble methods he uses.