If you select Use Standard Cost as the Default Price on Purchase Orders and Bills [System-Wide] (Setup > Preferences > Inventory), AccountEdge will use the Standard Cost you indicated in the item's Buying Details window when Purchase Orders or Bills are created, or $0 if you haven't entered a value.

Otherwise, AccountEdge will use the Last Purchase Price as the Default Price. The last purchase price is taken directly from the last bill the item was included on.

Either price model can be overridden before the Purchase Order or Bill is Recorded, however.