My guess (and it's just a guess) is that it's harder to make the skin units, especially the super thin ones. Lace is just people tying hairs in knots onto the lace but the super thin skin units have to have the hairs inserted with a lot of precision so they don't go through the skin. Even if they are done by machine, maybe there is a lot of setup time to get the machine and skin and hair ready for the process, and maybe they don't work out as often as skin units and starting again with a new set of materials has to be factored into the final price.