gistfile1.js

// ==UserScript==
// @name           Swoopo Ripoff Calculator
// @namespace      http://*.swoopo.com
// @include        http://www.swoopo.com/

// ==/UserScript==

var spans = document.getElementsByTagName("span");
var priceRe = /^price_index_page_.*/;
var earnRe = /^earn_price_index_page_.*/
setInterval(
       function() {

               for (i = 0; i < spans.length; i++) {

                               if(spans[i].getAttribute('id') != null && priceRe.exec(spans[i].getAttribute('id'))) {
                                       priceSpan = document.getElementById(spans[i].getAttribute('id'));
                                       earnSpan = document.getElementById('earn_' + spans[i].getAttribute('id'));
                                       if (earnSpan != null) {
                                               earnSpan.parentNode.removeChild(earnSpan);
                                       }
                                       //priceSpan.addEventListener('onchange', updateEarnings, false);
                                       priceString = priceSpan.innerHTML;
                                       price = parseFloat(priceString.substring(1));
                                       earnings = (price/0.12) * .60;
                                       roundedEarnings = Math.round(earnings*Math.pow(10,3))/Math.pow(10,3);
                                       
                                       //console.log("price: " + priceString + " earnings: $" + roundedEarnings);

                                       earningsSpan = document.createElement('span');
                                       earningsSpan.setAttribute('class', 'prd_pricetag');
                                       earningsSpan.setAttribute('id', 'earn_' + spans[i].getAttribute('id'));
                                       br = document.createElement('br');
                                       earningsText = document.createTextNode("$" + roundedEarnings);
                                       earningsSpan.appendChild(br);
                                       earningsSpan.appendChild(earningsText);

                                       //priceSpan.parentNode.appendChild(br);
                                       priceSpan.parentNode.appendChild(earningsSpan);

                               }
                       
               }

       },
       5000);