As far as price. They probably have a ton of leftover trimmings from GT carbon tube and carbon wheels. They probably chop this waste weave into loose fibers. So they're getting the filler for free or at least an extreme discount.
This in not woven carbon fiber sheets hand laid in a mold, epoxied and baked in an autoclave. It's not that "carbon fiber". It's loose carbon fibers suspended in plastic. Plastics have "fillers" most fillers are crushed rocks to give add weight. You know because things are bought and sold by...