When generating purchase orders in Accounts Payable, there is an option that directly controls whether the generated POs use the unit price from the approved Requisition or the default unit price on the product record.
 
When selecting to Generate Purchase Orders, on the General Tab, ensure that the option for "Do you want to override the unit price of the line item" is set to “Always use the unit price from the requisition line item” to ensure the PO is created with the edited price.