public function cost($origin, $originType, $destination, $destinationType, $weight, $courier) {
        $params = array(
            'origin' => $origin,
            'originType' => $originType,
            'destination' => $destination,
            'destinationType' => $destinationType,
            'weight' => $weight,
            'courier' => $courier
        );
        $rest_client = new RESTClient($this->api_key, 'cost', $this->account_type);
        return $rest_client->post($params);
    }