How did they work it out, do you know? Did they say?
I always think that statistics are a slippery subject. Obviously every bullet and bomb has a price, but a professional soldier costs much the same whether in his home country or abroad, aeroplanes and ships get out of date and lose value and utility.

I'm not condoning anything, but someone with an axe to grind will shove the cost of a standing army onto a war, and it is the standing army and its supplies that costs, more than the war. The machinery, structure, and personnel were already in place. Paid for.
Then there is the problem of disposing of depleted uranium. (if it isn't fired at enemy tanks.) Not to forget the extra jobs for people who make ammo.
I'd hate to be the accountant for a war, but better that than being one of the poor sods out there, on either side. I'll bet there were more punters than politicians killed.