Their margins on these sort of parts is quite large. I know, because I could replicate one of these as a one off, including hard-coating the aluminum, and molding and casting the parts, and it would come out in the ~$200 area.
I am very familiar in the metal mold and plastics industry as well as prototyping and if you are talking about simply copying the design by casting the parts in a silicone mold then molding parts from it in plastic then 200.00 to even 300.00 is a bit of a stretch, heck I know it is. That is not even including the time to measure out the center aluminum chassis and the machine time to make it.
If your talking about creating a one off design from a blank sheet of paper, when you consider design time and machine time and all the materials involved, you are not even in the same galaxy of around $200.00
This is why prototypes will always cost a fortune more than the actual production item.
Back to the topic though, I have a full blown CF option Anza Chassis for my so called Slash. If I do say so myself, asside from a few holes in the middle, that center aluminum chassis looks almost identical to the Anza one I have.