Inventory valuation with Project stock- project for long periods with same material

Hi Experts,

My client using PS and all process (Sales, production) will be linked to WBS.

Now we are facing problem with inventory valuation of FG, we are using valuation with specific to project.

Example- I have FG that is linked to one WBS element (Valuation is specific to project). On 1^st of September I have created one production order and done GRN for production order (GRN was happened with price 100, the price is the plan cost of production order. As a standard functionality it will check priority and taken plan cost of production order) and the same price 100 has been updated in table QBEW in the combination of WBS and Material. Like that in the month of September I have created 10 orders and done GRN.

Now in October also I have created one production order and done GRN, system still taking 100 for GRN (But in the month of October there is huge change in raw material prices), how can I update the price for this WBS and Material ( CK40N will not work because this is project stock and valuation also project).

Please help how can I change the price periodically in table QBEW.

Thanks,

Chandu