on select price change

<select class="form-control calculate" id="size" name="size">
    <option data-price="5.00" value="Small">Small</option>
    <option data-price="10.00" value="Medium">Medium</option>
    <option data-price="15.00" value="Large">Large</option>
</select>

<span id="item-price">00</span>

<script type="text/javascript" src="jquery-1.11.0.js"></script>
<script type="text/javascript">
var basePrice = 0;

$(".calculate").change(function () {
    newPrice = basePrice;
    $(".calculate option:selected").each(function () {
        newPrice += parseFloat($(this).data('price'));
        console.log(typeof newPrice);
    });
    newPrice = newPrice.toFixed(2);
    $("#item-price").html(newPrice);
});
</script>