<asp:DataGrid ID="miaGridView" runat="server" AutoGenerateColumns="true"  >
            <Columns>
                <asp:TemplateColumn>
                    <ItemTemplate>
                        <%# Convert.ToDouble(Eval("quantita")) *  Convert.ToDouble(Eval("prezzo")) %>
                    </ItemTemplate> 
                </asp:TemplateColumn> 
            </Columns>