Technical logic to captured the project cost

Dear Expert,

I would like to know about the technical logic of how we can get the project cost (i.e external purchase cost ) based on netwrok.In my scenario,I want to develop  one RFC capturing the project name,wbs,network,purchase order,material,qty,vendor and its cost by giving input of plant,posting date and purchasing org. Please share your thoughts and useful links for the same.I try to search it but didnt get.Thanks in advance.

Regards.

Swapnil