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;
$(".c