I don't recommend you do this but this is just an alternative way to do what you did with the if-else chain, of doom, in a smaller more compact version.

>var/global/list/sellable_items = list(/obj/item/weapon/coin/iron = 1, /obj/item/weapon/coin/plasma = 2)

and then loop through it like this:

>for(var/sell_type in sellable_items)
>    if(istype(A, sell_type))
>        plasma_count += coin_worth[sellable_items]


Now here is what I recommend you do and would be much better and make it much easier to sell items via cargo. Give every "obj" a "cargo_points" variable which you simply just use when selling an item. This can then be used for crates too.

>/obj/
>    var/cargo_points = 0

>/obj/structure/closet/crate
>    cargo_points = 5

>/obj/item/weapon/coin/iron
>    cargo_points = 1