<asp:GridView ID="MiscPayGridView" runat="server" ShowFooter="True">
 <asp:TemplateField HeaderText=" Total Expenses">
                            <ItemTemplate>
                                <%# Eval("totalexp", "{0:c}")%>
                            </ItemTemplate>
                            <FooterTemplate>
                                <asp:Label ID="lblSummary" runat="server" />
                            </FooterTemplate>
                        </asp:TemplateField>

 private decimal _TotalExpTotal = 0;

        protected void MiscPayGridView_RowDataBound(object sender, GridViewRowEventArgs e)
        {
            if (e.Row.RowType == DataControlRowType.DataRow)
            {
                decimal TotalExps = (decimal)DataBinder.Eval(e.Row.DataItem, "totalexp");
                _TotalExpTotal += TotalExps;
            }
            if (e.Row.RowType == DataControlRowType.Footer)
            {
                Label lblSummary = (Label)e.Row.FindControl("lblSummary");
                lblSummary.Text = String.Format("Total Exp: {0:c}", _TotalExpTotal);
            }
        }