The idea here is that cost is divided between the emplacement itself and the crew.
That allows unit preservation and better pricing.
For instance if the crew could abandoned the weapon and survive bombardments one could increase XP value and price for the package but lower the price for building the structure only.
That's actually a really interesting idea. Honestly I'd love to see it applied to all british emplacements: if you make them decrewable or whatever you can change them to be a lot less frustrating without making them even more useless than they already are, same goes for pak 43 and maybe even those flak guns okw can build doctrinally.