By default Microsoft Dynamics GP gets the Last Invoice Cost on a Purchase Order from Inventory setup in Cards | Inventory | Vendors.
If you would like the Last Invoice Cost to default from the Inventory Current Cost or Standard Cost you can do that with the free POP Cost Defaulter utility that is part of the Professional Services Tools Library (PSTL).
POP Cost Default is easy to use. Simply check the box next to the tool to activate it. Mark the radio button and hit next to set it up.
Setup is ridiculously easy. Pick where you want the cost to default from and click Ok.
That’s all there is to it to changing the source of your Last Invoice Cost on P.O.’s