Why are you interested in the cost of one particular now obsolete weapon?
Weapons go into and out of service all the time - as they are changed, upgraded, wear out, and so on. And of course there will always be disposal costs.
Are you interested in how much an artillery shell costs? - and how much it costs to dispose of them when the time comes? - and rifles, and etc etc?
Would you like to go through the whole defence budget line by line?
Do you think someone else could dispose of them more cheaply?
Or what exactly?