/**
  * Returns the sign up fee (excluding tax) by filtering the products price used in
  * @see WC_Product::get_price_excluding_tax( $qty )
  *
  * @return string
  */
 public function get_sign_up_fee_excluding_tax($qty = 1)
 {
     add_filter('woocommerce_get_price', array(&$this, 'get_sign_up_fee'), 100, 0);
     $sign_up_fee_excluding_tax = parent::get_price_excluding_tax($qty);
     remove_filter('woocommerce_get_price', array(&$this, 'get_sign_up_fee'), 100, 0);
     return $sign_up_fee_excluding_tax;
 }