I recently made a similar enquiry about having a new tartan woven through scotweb, and was quoted £57 a yard. After contacting a mill directly, I was given the price of £32 a yard, so a finished kilt works out cheaper than the cost of the scotweb material only.
My advice is that it pays to shop around.
This was for a self designed tartan, not one designed via scotweb, but registered with the tartan registry.