I handle this issue as follows:
 
PO-C process a negative qty receipt at the original wrong $ value.  This will create a negative $ entry in AP-C which can be offset against the original receipt at the wrong price by processing a $0 value invoice against this P.O.
 
Edit the P.O. item (PO-A) to the correct price and re-receive it in PO-C.  This will create another entry in AP-C at the correct price for which the actual invoice can be processed.
 
You will also see transactions in IN-A and IN-E for these 3 receipts, the last being the corrected $value and the average cost should now reflect the last receipt at the proper cost.

Yes, every time you go into PO-C and save a receipt, you will get a single BKAPHPO entry and a BKAPHPOL entry for each line received.  The scenario you describe should have 3 each.