imediasun1,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
</head>
<body>
<input type="checkbox" id="leter_registered" class="checkbox_prepay_delivery" name="leter_registered" checked="checked">
<label for="leter_registered"class="text" >Письмо заказное</label>
<input type="text"name=" leter_registered_price" class="input_price_delivery" size="5" value="12345">
<script>
$('.checkbox_prepay_delivery:checked').each(function(){
var label_check = $(this).nextAll('label');
var input_check = label_check.next();
alert([label_check.text(),input_check.val()])
})
</script>
</body>
</html>