[Триви]

Наговнокодил побыстрому пойдет?

<span>100$</span><input type="checkbox" onclick="sumUp();" /><br />
<span>210$</span><input type="checkbox" onclick="sumUp();" /><br />
<span>120$</span><input type="checkbox" onclick="sumUp();" /><hr />
<span id="result">0</span>$

<script type='text/javascript'>
var checkboxes = document.getElementsByTagName('input');
function sumUp() {
  var sum=0;
  for (var k in checkboxes)  {
      var checkbox = checkboxes[k];
      if(checkbox.type=='checkbox') {
        checkbox.checked==1 ? sum += parseInt(checkbox.previousSibling.innerHTML) : sum;
      }
  }
  document.getElementById('result').innerHTML = sum;
}
</script>