jQuery set value to delegated input fields

I have the HTML code as follows.

<table id="items">
 <tr class="item-row">
        <td class="item-name"><div class="delete-wpr"><a class="delete" href="javascript:;" title="Remove row">-</a></div></td>
        <td><input type="text" id="slslno" class="slno"/></td>
        <td><input type="text" class="cost"/></td>
        <td><input type="text" class="qty"/></td>
        <!--  <td><span class="price"></span></td>-->
        <td class="price"></td>
        <a class="add" id="addrow" href="javascript:;" title="Add a row">+</a> </tr>

</table>

It has a button named "Add a row" which adds more rows dynamically.

Then I have this bind, which calls an update function during blur of the slno field.

  function bind()
  {
      $(".slno").blur(update_unitcost);
  }

The function update_unitcost is as follows.

function update_unitcost()    
{
    var unitprice1=$(this).val();
    unitprice={"unitpricereal":unitprice1};
    $.ajax({
        type: "POST",
        url: "findcost.php",
        data: unitprice,        

        success: function(unitp){           
            $( ".cost" ).val(unitp);        
        }
    });                
}

In the above function, I am able to get the values of with the this selector, but when it comes to setting the value in the following line,

$( ".cost" ).val(unitp);

It just resets every ".cost" classes to that particular number. How can I set values to individual delegated rows? I tried the following approach too, but it failed.

 var row = $(this).parents('.item-row');
 row.find('.cost').val(unitp);

Set a variable in your function to only target the specific .cost element you wish to update instead of all of them.

function update_unitcost()    
{
    var unitprice1=$(this).val();
    var costItem = $(this).parent().parent().find('td input.cost');
    unitprice={"unitpricereal":unitprice1};
    $.ajax({
      type: "POST",
      url: "findcost.php",
      data: unitprice,        

      success: function(unitp){           
       costItem.val(unitp);        
      }
    });                
}