The PO is just an approval to purchase. It's the receiving transaction that is going to cause the problem.
What we would do is enter an inventory adjustment, cancel the payable, and reverse the original accrual if necessary.
You can enter another receiving for the correct price and receive against it so that your purchase history is correct.
If you need a new PO, just use the same PO number with a letter "A" at the end...the same with the vendor invoice.
Thanks!
Barb E.