Thanks for your response, Jim.
I used the Business Analytics WoC , though for the first time. I chose the "Purchase Order Item Details" as the Data Source. And was able to choose all the fields (other than the last one, which I just created by using formula in Excel) for my report from there.
A Correction: Please read Amount (Quantity x Rate) in the list of fields above.
Thanks again.
Regards
Yagyesh