随手一敲烂代码 哈哈哈  大概就是算差价再用jquery改变对应的内容
var success=function(result){
    if(result.state==1){
        $(function () {
            //原来的总价
            var total =  parseInt($("#total").html());
            //得到那个小计
            var price =parseInt($("#newsum-"+product_id).html());
            //得到和之前的差价
            var sub=result.sum-price;
            //得到新的总价
            var newtotal=total+sub;
            $("#newsum-"+product_id).html(result.sum);
            //修改总价
            $("#total").html(newtotal);
        });

<dd>
       <strong>购买数量：</strong>
        <input name="number" type="text" id="number"  onblur="changeNumber(<?php echo $data['id']?>,this.value)" value="1" size="4" onblur="" style="border:1px solid #ccc; "> <strong>商品总价：</strong><font id="totalPrice" class="f1">￥2588元</font>
       </dd>

<script type="text/javascript">
        function changeNumber(){
              var num = parseInt($("#number").val());
              var sellPrice = <?php echo $data['price']?>;
              $("#totalPrice").html("￥"+num*sellPrice+"元");
        }
      </script>

我是修改的产品页面中的总价格

我弄好了

你猜呀！