I propose you to invetigate 2 directions :
One is to use the continious production flow of SAP, that means that you have perhaps a defined number of finish product (not changing or slowly)
You will then use the cost object hierarchy to distribute the cost to the finish product… It’s done one’s a month, so it’s perhaps not what you wait.
The second is to take a totally different direction : work with configurable products. So with a few different product that you can adapt to the need (or the possible) you can go to the thrue finish product…
Each production order will give you its thrue cost, income & margin. Usually, it’s a make to order process (no make to stock)
I don’t know your business enough to give you more info. But I should be intersted to know your final choice.