[GM/TM] I need a script doctor

[MadameNova]

I found this neopian shop discounter someone made, but it does not seem to work. Could someone check it out when they get a chance?

// ==UserScript==
// @(you need an account to see links)        Neopets: Reduce Shop Prices
// @(you need an account to see links)space   userscripts-mirror.org
// @(you need an account to see links)cription Reduce prices in shop by specific percentage
// @include     (you need an account to see links)
// @include    (you need an account to see links)
// @include    (you need an account to see links)
// @require    (you need an account to see links)
// ==/UserScript==

$total = 0;
$items = 0;
var debug = false;

$("input[name^='cost']").each(function(){
    $amount = $(this).parent().parent().find('td:eq(2)').text();
    $amount = Number($amount);
    $thisItem = 0;
    for(var i = 1;i <= $amount;i++){
        $thisItem = $thisItem + Number($(this).val());
    }
    $total = $thisItem + $total;
    $items++;
});

// alert($test);

$total = $total.toString().replace(/\B(?=(?:\d{3})+(?!\d))/g, ",");

GM_log($total);
GM_log($items);

$("center:contains('Items Stocked')").append("<br>Total : <b>" + $total + " NP</b>");

// code to insert checkbox
// Round to nearest 100?<input type='checkbox' name='round' checked><br>

$("tbody:contains('Piccy'):last tr:contains('Remove All'):last").before("<tr><td colspan='8' bgcolor='#dddd77' align='center'><input type='text' value='10%' id='discount' size='3'><input type='button' value='Discount Prices' id='discountUpdate'></td></tr>");

// alert("Shop Total: "+$total+"NP");

$("#discountUpdate").click(function(){
    $discount = $('#discount').val();
    $discount = $discount.replace('%','');
    if($discount < 100){    
        $discount = $discount / 100;
        // check if checkbox is checked, if yes, round discount, if not, continue normally
        if(debug){GM_log($discount);}
        $("input[name^='cost']").each(function(){
            $currentPrice = $(this).val();
            if(debug){GM_log("Current: " + $currentPrice);}
            if($currentPrice != 0){
                $newPrice = Math.round($currentPrice - ($currentPrice * $discount));
                if(debug){GM_log("New (discounted by 10%): " + $newPrice);}
                $(this).val($newPrice);
            }
        });
        alert("Prices discounted! Remember to update the shop!");
    }else{
        alert("Please input a percent under 100");
    }
});