DropDownList validation inside GridView using jQuery in ASP.Net

I have a dropdownlist inside a gridview,the drop list should populate from database and default value should be SELECT.

when i Click Save button it should check all the dropdownlist values. If any one is still SELECT it should prompt error select any values.

When i normaly check without inside gridview it works fine and not inside gridview.

I have attached my codings below.

Help in this regard.

Thanks

<asp:GridView ID="GVResrv" runat="server" Width="100%" AutoGenerateColumns="false"
    TabIndex="1" Font-Names="Times New Roman" Font-Size="Smaller" HeaderStyle-HorizontalAlign="Center">
    <Columns>
        <asp:CommandField ShowSelectButton="true" HeaderText="Details" SelectText="Details" />
        <asp:TemplateField>
            <HeaderTemplate>
                <asp:CheckBox ID="chkHeader" runat="server" Checked="true" />
            </HeaderTemplate>
            <ItemTemplate>
                <asp:CheckBox ID="chkRow" runat="server" Checked="true" />
            </ItemTemplate>
        </asp:TemplateField>
        <asp:BoundField DataField="Vin" HeaderText="VinNumber" />
        <asp:TemplateField HeaderText="Sales Person">
            <ItemTemplate>
                <asp:TextBox ID="txtSalesPersonName" runat="server" Text='<%# Eval("Sales_Person_Name") %>' />
            </ItemTemplate>
            <ItemTemplate>
                <asp:DropDownList ID="ddlSalesPerson" runat="server" DataSourceID="SqlDataSource2"
                    DataTextField="SalesPersonName" DataValueField="SalesPersonName" AppendDataBoundItems="true">
                    <asp:ListItem Text="SELECT" Value="0" />
                </asp:DropDownList>
                <asp:SqlDataSource ID="SqlDataSource2" runat="server" ConnectionString="<%$ ConnectionStrings:VehicleConnectionString %>"
                    SelectCommand="Select SPNID,SalesPersonName from R_ResrvSalesPerson"></asp:SqlDataSource>
            </ItemTemplate>
        </asp:TemplateField>
</asp:GridView>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js"></script>
<script type="text/javascript">
    $(document).ready(function () {
        $("[id$=btnSave]").click(function () {
            if ($("[id$=ddlSalesPerson]").val() != 0) {
                //Selected option from dropdownlist


                return true;
            } else {
                //Not selected so alert user to select any option

                alert('Please select Sales Person Name');
                return false;
            }
        });
    });
</script>