Yes carbon is expensive, but it’s properties, make just a few layers of the stuff equal to, the use of more of the other materials.
For eg. The amount of layers of carbon of a given weight, to rival the stiffness of glass of a given weight, is not as much. Because there is fewer layers, there is less resin used. The costs just about match up overall.
Also, this is how using carbon makes things light, because not much of it is needed etc.
As for making boats expensive, it’s not the materials. It’s the time spent on the nessesary steps, to making craft to very high calibers. With carbon, the structural reinforcement is seen, and to build with the stuff to have good strength, and good looks, makes the craft tricky. An easy way is to hide it all with a thick gelcoat. Then the extra care in using the fibers is not needed (prices drop down).
Molding the parts is easy, building them together in the right places, and the the fine tuning of the assembled parts (fairing, alignment, and such), is what makes a product expensive.
I had some one ask me to caculate making them a rig, like the ones on my personal boats. There’s to much hourly detail work to sell them. The spars and the fishing hardware supplies are cheap, but filiment winding them into place, with all the wee bits, and micro-fairing the wee fillets, is a lot of hand work.
Bond some slabs of balsa together is one price. Sanding, shaping, sculpting, and finishing the surface to reflect one’s image is another.