You would have to pay for them to measure andale a digital copy. Or atleast break it down to do it by hand (whatever method your shop uses).
But you also have the cost of the header to copy. So $400 + labor to copy + labor to build each one + cost of materials divided by number of orders. Just the @$400 for the first header = $40 per person tacked onto the group buy if you have 10 orders.