Using a MIN, MAX formula on a calculated field in a pivot table
 

How can I create a calculated field that includes formulas with MIN, MAX or
AVERAGE?
Becasue the summary form calculated field of a pivot table cannot be changed
(is always SUM), Excel returns a different number when I try to insert a
field that includes such a formula.
I am trying to include a field like this to calculate minimum possible cost:
=MIN('Price')*SUM(Order Quantity)
Any suggestion on how to do it?