drop down price summing

with pure Javascript, get values of drop downs and sum price below.

HTML

<form action="" id="orderForm" name="orderForm">
  <select id="itemSize" name='itemSize' onchange="getTotal()">
    <!-- query for all data with pid=id of product and category = 'a' so select id and name are dynamic -->
    <option value="2">2oz</option>
    <option value="4">4oz</option>
    <option value="8">8oz</option>
    <!-- Value is dynamic as is the inner data ie. 2oz, 4oz, etc. can range from sizes, color, metal types, etc. -->
  </select>
  <select id="quantity" name='quantity' onchange="getTotal()">
    <option value="1">1</option>
    <option value="2">2</option>
    <option value="3">3</option>
  </select>
  <select id="metal" name='metal' onchange="getTotal()">
    <option value="10">Silver</option>
    <option value="20">Gold</option>
    <option value="30">Platinum</option>
  </select>
</form>
<h3 id="totalPrice"></h3>

JavaScript

function getDDValue(elementID) {
  var value = 0;
  var element = document.getElementById(elementID);
  value = element.options[element.selectedIndex].value;
  console.log(value);
  return parseFloat(value);
}

function getTotal() {
  var itemSize = getDDValue("itemSize");
  var quantity = getDDValue("quantity");
  var metal = getDDValue("metal");
  var totalPrice = '0';

  totalPrice = metal + itemSize;
  totalPrice = totalPrice * quantity;
  console.log(totalPrice);
  document.getElementById('totalPrice').innerHTML = "Total Price $" + totalPrice;
}

getTotal();