JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://code.jquery.com/jquery-migrate-1.2.1.min.js"></script>
<label id="item">0</label>
<form action="" id="bestelformulier">
  <select id="personen">
    <option value="0">Aantal personen</option>
    <option value="1">1 Persoon</option>
    <option value="2">2 Personen</option>
    <option value="3">3 Personen</option>
    <option value="4">4 Personen</option>
    <option value="5">5 Personen</option>
    <option value="6">6 Personen</option>
    <option value="7">7 Personen</option> 
  </select>
  
  
  <select id="product1">
    <option value="0">Geen</option>
    <option value="1">1 stuk</option>
    <option value="2">2 stuks</option>
    <option value="3">3 stuks</option>
    <option value="4">4 stuks</option>
    <option value="5">5 stuks</option>
    <option value="6">6 stuks</option>
    <option value="7">7 stuks</option>
  </select>
  
  
  <select id="product2">
    <option value="0">Geen</option>
    <option value="1">1 stuk</option>
    <option value="2">2 stuks</option>
    <option value="3">3 stuks</option>
    <option value="4">4 stuks</option>
    <option value="5">5 stuks</option>
    <option value="6">6 stuks</option>
    <option value="7">7 stuks</option>
  </select>
  
  <select id="product3">
    <option value="0">Geen</option>
    <option value="1">1 stuk</option>
    <option value="2">2 stuks</option>
    <option value="3">3 stuks</option>
    <option value="4">4 stuks</option>
    <option value="5">5 stuks</option>
    <option value="6">6 stuks</option>
    <option value="7">7 stuks</option>
  </select>
  <input type="submit" value="Verstuur" />
</form>

<div id="aantalProducten"></div>
<div id="melding"></div>

JavaScript

var total = 0;
var hideAllAfterTotal = function(){
  var o = $(this), v = parseInt(this.value); 
  if(v > total) o.hide();
  else o.show();
};
$('#product1 > option').each(hideAllAfterTotal);
$('#product2 > option').each(hideAllAfterTotal);
$('#product3 > option').each(hideAllAfterTotal);

var berekenTotaal = function(){
  var s = $(this), i = this.id, v = parseInt(this.value);
  if(i == 'personen'){
    total = v;
  } else {
    total -= v;
  }
  $('#product1 > option').each(hideAllAfterTotal);
  $('#product2 > option').each(hideAllAfterTotal);
  $('#product3 > option').each(hideAllAfterTotal);
  $('#item').text(total);
};

$('#bestelformulier').on('submit', function(){return false;});

$('select').on('change', berekenTotaal);