CheckBox - Sum Values To Textbox When Checked

The problem I have is that the value="" needs to be the ID number of the recordset but still be able to SUM the dollar value on the TEXT box (totalcost) when someone click on each CHECKBOX. The CHECKBOX values will be coming out of a database using PHP. How do I modify the Javascript to accomplish what I'm looking for.

Code:
<script type="text/javascript">
function UpdateCost() {
var sum = 0;
var gn, elem;
for (i=0; i<5; i++) {
gn = 'game'+i;
elem = document.getElementById(gn);
if (elem.checked == true) { sum += Number(elem.value); }
}document.getElementById('totalcost').value = sum.toFixed(2);
}
</script>
<form action="<?php echo $editFormAction; ?>" method="POST" name="form1" id="form1">
<input type="checkbox" id='game0' value="9.99" onclick="UpdateCost()">Game 1 ( 9.99)<br>
<input type="checkbox" id='game1' value="19.99" onclick="UpdateCost()">Game 2 (19.99)<br>
<input type="checkbox" id='game2' value="27.50" onclick="UpdateCost()">Game 3 (27.50)<br>
<input type="checkbox" id='game3' value="45.65" onclick="UpdateCost()">Game 4 (45.65)<br>
<input type="checkbox" id='game4' value="87.20" onclick="UpdateCost()">Game 5 (87.20)<br>
<input type="text" id="totalcost" value="">
</form>