It strikes me cats are looking for three things from a mast, lowest weight, adequate stiffness and an aerodynamic shape. With a cat without spreaders ignoring the aerodynamics the most efficient shape is a tube and there is a cheap source of carbon fibre tube. That is pullwound tube.

I beleive that comes out to around $50/kg for bulk purchase so for a 15kg mast that is $750.

This would sort out the low weight and high stiffness. Perhaps you could than get the aeroshape by adding some other cheaper appendage. You would also have to add a mast track. But its still coming out well below $3000 and there is no tooling cost to cope with.