Use the innovatve LC-1 it is $150 for the controller, and $45 dollars for the wideband sensor which you get get at any VW dealership or right on innovative's main site

http://www.innovatemotorsports.com/products/lc1.php

You can buy gauges or just use a laptop to monitor afr ranges. Have you ever tried to stare at a gauge at full boost and full RPM? It's not that easy and may give you shifty results. I would stay with the laptop and use the realtime graph software included to save money.