I can't look at the ebay link from work but in my opinion getting a WBo2 is very important for turbo tuning. The WBo2 that people have linked to up there all use the NTK L1H1 WBo2 sensor. This is a VERY expensive sensor (like $200). There are other WBo2 options that use the Bosch LSU4 sensor. They are the Zeitronix ZT-2 and the AEM UEGO to name a few. This sensor is MUCH cheaper ($80) to replace and is just as accurate. You'll just be hard pressed to find a DIY solution for it but the current controllers using it are reasonably priced. I'm sure you could find more doing a search on google (try many variations in the search field).