Hi Samiullah,
If we upload the balance in previous month and the material price is 0, then your stock value is 0. If you run cost estimation for Jan month, then your stock will get revaluated with the new price.
However, If you do not want to post the stock value in Jan month, then first you have maintain the price by MR21 for the Dec month and upload the balance. After that you run cost estimation for Jan month, then any price variance happened with costing, then it will valuate the inventory accordingly in Jan month.
Regards,
Mukthar