There are 2 different suppliers of different territory for 1 item.Both the suppliers have different price range depending upon quantity, say Price A and Price B.
Create pricing template and select appropriate as per the Qty posted into the PO. For better naming point, state the qty range in the name of Pricing rule, so that user does not make error in selecting right template.
I’m not sure, if you looking for is auto selection of correct price rule from defined template. Maybe that would be achievable by writing custom script.