JSFiddle - React, Tailwind, and code Playground

HTML

<form>
  <p>
    <label>Alhambra : 816</label>
    <input onchange="prix()" type="radio" value="816" id="alhambra" name="monuments" />
    <label>Helios : 1594</label>
    <input onchange="prix()" type="radio" value="1594" id="helios" name="monuments" />
  </p>

  <p>
    <label>Tarn : 300</label>
    <input onchange="prix()" type="radio" value="300" id="tarn" name="granits" />
    <label>Dalva : 400</label>
    <input onchange="prix()" type="radio" value="400" id="dalva" name="granits" />
  </p>

</form>

<p>
  Prix : <span id="texte">0</span>
</p>

JavaScript

function prix() {
  var monuments = document.getElementsByName("monuments");
  var granits = document.getElementsByName("granits");
  var valeur = 0;
  for (i = 0; i < monuments.length; i++) {
    if (monuments[i].checked) {
      valeur += parseInt(monuments[i].value);
    }
  }
  
  for (i = 0; i < granits.length; i++) {
    if (granits[i].checked) {
      valeur += parseInt(granits[i].value);

    }
  }
  document.getElementById('texte').innerHTML = valeur;
}