I hope they were showing the Bathurst race that was held last weekend. Perhaps in the top 5 street circuits in the world....
I think I read that the used Winston Cup cars generally go for $40 to $60K complete? If the engine has been freshened, there's no way that you'd get a V8 Supercar for anywhere near that. Reco'd engines over here (done right) cost about $35 to $40K USD on their own...
A V8 Supercar would make a Cup car look pretty silly on a roadrace track.
Get them on an oval and it'd be a different story though - but going round and round in circles doesn't look like much fun!
Craig