Sales Order Costing (Project Scenerio)

Dear All,

I am doing (MTO) sales order costing (Account Assignment is WBS element).

Material Code XYZ contains raw material X,Y,Z.

XYZ=XYZ and price in Material master price control (V) - 50,100,150 price for X,Y,Z.

So when I does Sales order Costing XYZ=50100150

XYZ=300

Requirement comes from Sales order and when GR will done system will have new price for mareial

X=100,Y=200,Z=300. So when production order confirm the actual cost of the material =100200300

= 600

But,system is giving XYZ=50100150

XYZ=300.

Please guide me how to get actual cost 600 instead of 300.

Regards

Sainath