My car had the rear springs replaced by the former owner and I have a bill for £285.00 from the dealer. I looked at a 3.0 car before buying the one i eventually got and he too had an invoice for nearly £300.00. sounds about the going rate
It does annoy me that they only seem to do one side under warantee... you will have all the pain of taking it to them again when the other side goes twang (not to mention spings sag over age and could have a odd ride height).