PHP - Ajax Drop-Down field save all the values instead of selected value

#1

Here my form auto responce based on drop-down list,

  <tr> 
    <th>Shipping Cost (Rs) : </th> 
   <td id="findata"></td> 
   <input type="hidden" name="shipping_cost"  id="shipping_cost"/>
   </tr>
<tr>

Same page Ajax :

<script>
    $(document).ready(function(){
    $('#new').on('change',function(){
    var zip = $("#zip_postal_code").val();
    var country = $("#country").val();
    $.ajax({
    type: "POST",
    // url: "ajax_ship_cost_data.php",
    url: "sp_cost.php",
    dataType: "text",
    data: { zip_postal_code: zip, country: country},
    success: function(data)
    {
        // Check the output of ajax call on firebug console
         //console.log(data);
        $('#findata').html(data);
        $('#shipping_cost').val(data);
    }

});
});
});

The field Shipping Cost is auto responce based following field,

<tr> 
<th>I have : </th> <td> 
<select id="old" name="i_have"> 
<option value = "select_option">Select Option</option> 
<option value = "three_compact">3 Compact</option>
<option value = "three_regular">3 Regular</option> 
<option value = "three_triple">3 Triple</option> 
<option value = "five_compact">5 Compact</option>
<option value = "five_regular">5 Regular</option>
<option value = "five_triple">5 Triple</option> 
<option value = "seven_compact">7 Compact</option>
<option value = "seven_regular">7 Regular</option> 
<option value = "seven_triple">7 Triple</option> 
<option value = "nine_compact">9 Compact</option>
<option value = "nine_regular">9 Regular</option>
<option value = "nine_triple">9 Triple</option>
</select> </td>
</tr>
<tr> 
<th>I want : </th>
<td> <select id="new" name="i_want"> 
<option value = "select_option">Select Option</option>
<option value = "three_compact">3 Compact</option>
<option value = "three_regular">3 Regular</option>
<option value = "three_triple">3 Triple</option> 
<option value = "five_compact">5 Compact</option>
<option value = "five_regular">5 Regular</option>
<option value = "five_triple">5 Triple</option> 
<option value = "seven_compact">7 Compact</option> 
<option value = "seven_regular">7 Regular</option> 
<option value = "seven_triple">7 Triple</option>
<option value = "nine_compact">9 Compact</option>
<option value = "nine_regular">9 Regular</option>
<option value = "nine_triple">9 Triple</option>
</select> </td> </tr>

I have writtend PHP logic like if I have & I want dropdown selected based on this i need to be given shipping cost, i did get the value from magento and shown to customer, if customer choose any one hipping cost dropdown value all values stored into to my table. How to avoid all values stored instead of selected value from ajax dropdown.

Shipping Cost PHP function,

<?php 

{
// LOGIC
}

Post
if(isset($_POST['zip_postal_code']) && isset($_POST['country']))
    {
     $zip_postal_code = $_POST['zip_postal_code'];
     $country = $_POST['country'];
}
$results = getShippingEstimate('14419','1',$country,$zip_postal_code);
###### Post #######
$count = -1;
echo "<select name='shipping_cost'>";
foreach ($results as $result): 
$count++;
?> <option value="<?php echo $count; ?>"> <?php echo $result["Title"]." - Rs ".$result["Price"];?> </option> <?php
endforeach;
echo "</select>"; 
?> 

Responce : https://snag.gy/8Yuev6.jpg

Expected result : Select and save selected value from dropdown instead of all values in drop down list.