Hope your sitting down! I had a quote from Southampton audi to replace a noisy tensioner and that was £3,149.51 would probably be more for a complete timing chain over hall
Although the service book states 85k when you speak to audi they claim that the chains are lifetime so they don't have to be changed. So unless you have a problem then there is no need to have them serviced. Even if you have the start up rattle even audi thinks this is normal. Just make sure you change the oil frequently, mine was on audi long life servicing before the tensioner went and I think the fact the oil wasn't changed for 20k was a contributing factor. So now I change my oil every 5k