Hi,
Goto SE16 / SE11/ SE16N ....enter table name MSEG- Material doc
enter Input as PO number or GRN number & you will get details
Aslo BSEG - Accounting document, EKBE- PO history.
better.....you can use standard T-code: ME80FN where you will get all the details PO history,GRN price,MIRO in change View tab.
Thanks & Regards,
Prashant