var ItemProps = new Class ({
 Implements: [Options],
 
 options: {
  priceId: null,
  propsClass: null
 },
 
 elements: {
  props: null,
  price: null
 },

 initialize: function(options) {
  this.setOptions(options);
  
  this.elements.props = $$(this.options.propsClass);
  this.elements.price = $(this.options.priceId);
  
  this.elements.props.addEvent("change", function() {
    this.updatePrice();
  }.bind(this)); 
  
  this.updatePrice();
 },
 
 updatePrice: function() {
  var sel = this.elements.props.filter(":checked");
  var price = sel.getParent().getElement("b").get("html");
  this.elements.price.set("html", price);
 }
 
 
});