Hi Vinoth,
First you maintain info record for material or without material (could be for service also, depending upon how you define it). On the basis of the same you create outline agreement. This means the prices valid at that time are copied to outline agreement. You can compare the PO price to Invoice price in report like MC$<.
On the other hand you can have outline agreement without info record. In this case with what you want to compare the prices a mentioned before and after creation of outline agreement?
Let me know if it helped.
Regards
Rahul