Further, a modern conventional symmetric war is unlikely to be long enough for cost to matter. Modern weapon systems are simply too expensive and time-consuming to build. There will be a few decisive battles, one side will lose most/all of their modern gear, and will be unable to replace it fast enough to continue the war. It's not like in WW2 where they were churning out a Liberty ship every week or a Sherman tank every 30 minutes.
I disagree with modern conflicts being short by nature.
Yes the pattern where you have a modern army vs a semi-modern one ( like Iraq or Egypt ) and a limited geographical area of conflict tend to be over very quickly, but no one in their right mind though a Soviet attack on Western Europe would be over or decided in a day or a week had it materialized during the cold war.
If we move forward to today's tech what happens when two equal sides fight a conventional war and both start by shooting down or disabling all the opponents satellites for Coms, Recon and even GPS? What happens when no or very few missiles or strike planes can get through to hit key targets because of the dense layers of SAM, Interception, E-War and Point defense? What happens when neither side can deploy troops, supplies and equipment the fast way with air-lift right to the frontlines due to the risks involved, and anything shipped must be coordinated to be heavily escorted?
Sure state of the art tech nations today have the tech to win quickly vs a WW2 tech level enemy or even a semi-modern one, but they also have invested just as much in denying a more equal tech enemy the ability to use that all that fancy tech...
The aurora equivalent is a fight where neither side have the missile numbers to deal a decisive knock out strike but PD, AMMs and shields handle 99% of them... Then a decisive war can only happen if both sides risk their valuable assets in a close range knife fight, and if either side has a clear advantage in a close range engagement the other side ( in reality ) is very likely to have the ability and means to avoid it and return to within own territory.
Such a war is decided by how deep the strategic stockpiles of missiles are, how much the factories can output once you know more about what equipment you actually need to gain an advantage and by the boots on the ground, all which will take time. About stuff being expensive and time consuming to build that's what people said before WW2 as well, but changed priorities increased production output level by 1000-fold and reduced time from order to delivery by 10-fold in many cases. Before WW2 there were about 40 million passenger cars in USA, today there are over 200 million despite each car of today being endlessly more high tech, so I don't think more advanced equipment necessitates smaller production numbers at all if priorities were set to military production instead of civilian.
Due to MAD and economical inter-dependencies on Earth today I think it's pretty unlikely we would see such a war happen though.