Normally this would simply require the repetition of the expression used to return the Current Stock values in the group footer, either in the Report Footer, or in a higher level group footer.
Note that values cannot be aggregated directly in a Page Footer. To return page totals use an unbound control in the Page Footer, and initialise and increment the values per page in the report's module, as in the example below:
Private Sub PageHeaderSection_Print(Cancel As Integer, PrintCount As Integer)
'reinitialise page total control to zero
Me.txtPageTotal = 0
End Sub
Private Sub Detail_Print(Cancel As Integer, PrintCount As Integer)
If PrintCount = 1 Then
Me.txtPageTotal = Me.txtPageTotal + Me.PaymentAmount
End If
End Sub