Well, first you look at the per-unit price of a Javelin shot.
The you look at a realistic storage life (not the shelf life that can be extended by an inspection) or if you dare to complicate the calculation even more: The life expectation as a 1st rate AT munition (about 15 years usually).
Then you look at the time that has already gone past and depreciate accordingly. That can take about 5-10 years off that Javelin, about half of the price.
Yet this calculation was only relevant if you expect to need the munition in another conflict or to replace it with a new round.
The cost of the round is zero if you won't do either. This is one of the great lessons of economic science; it helps us to be rational about this instead of trusting our guts (if we are informed).
The key here is that the money was already spent - sunk costs. Sunk costs must never be considered in a decision - they's past, sun, irrelevant.
Only opportunity costs (we would have needed that round in a later conflict) or replacement costs would be relevant.
Finally a last, unrealistic and thus irrelevant complication: The opportunity cost could also be positive if you would have sold that round. That does never seem to happen and is thus irrelevant.
In short: The Javelin shot was most likely dirt cheap.
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Now about force planning. That is a different game, it's about the decision to buy munitions. Nobody buys Javelins to bust bunkers (I hope - the Russians offered thermobaric Krizanthemas, though). These munitions are usually bought for other purposes and their use against low value targets is usually just an improvisation.
The typical dedicated anti-bunker munition is an unguided 300-600m Panzerfaust or Bazooka.
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Personally I wonder why people keep carrying such heavy munitions in AFG. Even a M136 is quite heavy. The Javelin firing post has a great thermal sight (if you have the batteries to run it) and may be justified as a platoon thermal sensor - but the missiles are odd.
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