How to control PO price and AP Invoice PRICE should be equal in R12

Hi Every one....

Being year end all users are  very active to clear their  entries.

Our  finance user run trial balance report  today . He got  surprise by noticing that   'Advance to Supplier'  show  huge difference compare to yesterday -  100K + more than previous day.

Upon checking we  found   AP user   booked one purchase invoice in that  he mentioned  unit price  as 200   instead of 100  (  PO  item unit price is  100 ). As  qty is more than 1000  the value also getting more

After spending  hours , we identified this user  user error.

Is there any way  -can we control -  AP Invoice  Unit Price should be same as PO  UNIT Price.