I don't know nearly enough about weaving to discuss what causes the high cost of the material. Perhaps I should call it the seemingly high cost, as I personally have nothing to truly compare it to. In any case, the materials seem to be the main factor in cost.

Hand sewn kilts take a lot of time to create but the kilt makers sure aren't getting rich off of their labor charges. Machine-sewn kilts are less expensive, but if they're using the Scottish worsted wool, you're still looking at a fair bit of money regardless of labor costs.