A few quid. Most wheel places do them or Halfords sell some. Demon Tweeks etc... Providing they are less than about 7mm they don't need to be hub centric as the wheel will still locate on the hub.. bigger than that and you'll need to pay more for them
I see, ta for the info Im still aiming towards RS4 replicas....yeah not very original but they look great and 18" wit tyres for under 500 delivered is mint!