Afficher le montant de façon automatique

<script type='text/javascript'>
 
			function getXhr(){
                                var xhr = null; 
				if(window.XMLHttpRequest) // Firefox et autres
				   xhr = new XMLHttpRequest(); 
				else if(window.ActiveXObject){ // Internet Explorer 
				   try {
			                xhr = new ActiveXObject("Msxml2.XMLHTTP");
			            } catch (e) {
			                xhr = new ActiveXObject("Microsoft.XMLHTTP");
			            }
				}
				else { // XMLHttpRequest non supporté par le navigateur 
				   alert("Votre navigateur ne supporte pas les objets XMLHTTPRequest..."); 
				   xhr = false; 
				} 
                                return xhr;
			}
 
			/**
			* Méthode qui sera appelée sur le click du bouton
			*/
			function go(){
				var xhr = getXhr();
				// On défini ce qu'on va faire quand on aura la réponse
				xhr.onreadystatechange = function(){
					// On ne fait quelque chose que si on a tout reçu et que le serveur est ok
					if(xhr.readyState == 4 && xhr.status == 200){
						leselect = xhr.responseText;
						// On se sert de innerHTML pour rajouter les options a la liste
						document.getElementById('nuitee').innerHTML = leselect;
					}
				}
 
				// Ici on va voir comment faire du post
				xhr.open("POST","ajaxLivre.php",true);
				// ne pas oublier ça pour le post
				xhr.setRequestHeader('Content-Type','application/x-www-form-urlencoded');
				// ne pas oublier de poster les arguments
				// ici, l'id de l'auteur
				sel = document.getElementById('formule');
				idauteur = sel.options[sel.selectedIndex].value;
				xhr.send("idform="+idform);
			}
		</script>

    <?php 
								//   $output = '';  
								//   $query = "SELECT * FROM formula WHERE id_user = '$pid'";  
							//	 $result = mysqli_query($conna, $query); 
								// 
									 		$res = "SELECT * FROM formula";
												$result = mysqli_query($conna, $res); 
					
				
         if(mysqli_num_rows($result) > 0)  {
								
	
								
								
								
								?>
								<strong class="text-muted d-block mb-2">FORMULE</strong>
								<div class="form-row">
                  
                              <div class="form-group col-md-12">
                                <select id='formule' class="form-control"  name="nafor"  onchange='go()'>
                                  <option selected   value='-1'>Choisir la formule</option>
								    <?php  while ($row = mysqli_fetch_array($result)){   
								
									
										?>
                                  <option  value = "<?php   
									   // echo $row["type"] ; echo "|";   echo $row["nuitee"] ; echo "|";  echo $row["montant"] ;
									   echo $row["id"];
										?>">
								  <?php 
								  //echo $row["type"] ; echo "|";   echo $row["nuitee"] ; echo "|";  echo $row["montant"] ;
								  echo $row["libelle"];
					}
								 } 
	?>
	  </option>
                                </select>
                              </div>
                            </div> 
								<div class="form-row">
							<div id='nuitee' style='display:inline'>
				<select name='livre'>
					<option value='-1'>Choisir nuitee</option>
				</select>
				</div>     </div> 

<?php
	echo "<select name='livre'>";
	if(isset($_POST["idform"])){
						$conn = new mysqli('localhost', 'ee', 'eee', 'eee');
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}
		$res = mysqli_query("SELECT id,montant FROM formul 
			WHERE idform=".$_POST["idform"]."");
		while($row = mysqli_fetch_assoc($res)){
			echo "<option value='".$row["id"]."'>".$row["montant"]."</option>";
		}
	}
	echo "</select>";
?>

[
 {
  "id":"1",
  "name":"SINGLE",
  "parent_id":"0"
 }, 
 {
  "id":"2",
  "name":"COUPLE",
  "parent_id":"0"
 }, 

 {
  "id":"4",
  "name":"1 nuitee",
  "parent_id":"1"
 }, 
 {
  "id":"5",
  "name":"2 nuitees",
  "parent_id":"1"
 }, 
 {
  "id":"6",
  "name":"3 nuitees",
  "parent_id":"1"
 }, 
 {
  "id":"7",
  "name":"1 nuitee",
  "parent_id":"2"
 }, 
 {
  "id":"8",
  "name":"2 nuitees",
  "parent_id":"2"
 }, 
  {
  "id":"9",
  "name":"3 nuitees",
  "parent_id":"2"
 }, 
 {
  "id":"10",
  "name":"194400",
  "parent_id":"4"
 }, 
 {
  "id":"11",
  "name":"249400",
  "parent_id":"5"
 }, 
 
]

 <script>
$(document).ready(function(){

 load_json_data('country');

 function load_json_data(id, parent_id)
 {
  var html_code = '';
  $.getJSON('country_state_city.json', function(data){

   html_code += '<option value="">Select '+id+'</option>';
   $.each(data, function(key, value){
    if(id == 'country')
    {
     if(value.parent_id == '0')
     {
      html_code += '<option value="'+value.id+'">'+value.name+'</option>';
     }
    }
    else
    {
     if(value.parent_id == parent_id)
     {
      html_code += '<option value="'+value.id+'">'+value.name+'</option>';
     }
    }
   });
   $('#'+id).html(html_code);
  });

 }

 $(document).on('change', '#country', function(){
  var country_id = $(this).val();
  if(country_id != '')
  {
   load_json_data('state', country_id);
  }
  else
  {
   $('#state').html('<option value="">Select state</option>');
   $('#city').html('<option value="">Select city</option>');
  }
 });
 $(document).on('change', '#state', function(){
  var state_id = $(this).val();
  if(state_id != '')
  {
   load_json_data('city', state_id);
  }
  else
  {
   $('#city').html('<option value="">Select city</option>');
  }
 });
});
</script> 

<div class="form-group col-md-12">
                                <select  class="form-control"   id="country"  name="nafor"  onchange='go()'>
                                  <option selected   value="">Choisir la formule</option>
								   
                
                                </select>
                              </div>
                            </div> 
							  <br />
							  <strong class="text-muted d-block mb-2">NOMBRE NUITEE</strong>
								<div class="form-row">
                  
                              <div class="form-group col-md-12">
                                <select  class="form-control"   id="state"  name="nafor"  onchange='go()'>
                                  <option selected   value="">Choisir le nombre</option>
								   
                
                                </select>
                              </div>
                            </div> <br />
							  <strong class="text-muted d-block mb-2">MONTANT</strong>
								<div class="form-row">
                  
                              <div class="form-group col-md-12">
                                <select  class="form-control"    id="city" name="nafor"  onchange='go()'>
                                  <option selected   value="">Choisir le nombre</option>
								   
                
                                </select>
                              </div>
                            </div> <br />