Anshul,
Have you tried maintaining the VPRS condition type in the material master? This is the standard condition type provided by SAP to maintain the cost price and it will flow into the sales order.
These values (Sales & Cost price) will be captured in the KONV table. You could then link VBAK, VBAP & KONV tables and build the custom report that you desire.
Hope this helps,
Ravin