By the time we get to the bottom of the list (1.5k or so as long as they don’t loose their place in line) they should be able to make the much cheaper than when they started. That is when any new buyers can even get one.
My approach would be to price the truck on the higher side to offset the cost to produce, then move down as costs improved. The caveat would be to start at the top of the list and move down but give the order holders the opportunity to pass but not lose their spot. Then for ever cost reduction...