Cost is unit responsibility and it seems to depend who's in the headquarters. If approval is given too far down the food chain there is always the risk of an irate AOC who doesn't like it and demands it is all taken off. There may well be an official way of approving them, but I can't recall ever seeing it in action. With hubs and spokes these days I would have thought the force commander would probably give it the nod and accept any flak later when it's too late.