Will vary, but on my bumper quests.
Ive found an S3 delivered, supposedly mint, for 250
An S Line Black Edition far from mint, has sensor holes etc, 195 + delivery.
On ebay now is a 2007 S3 for 300 delivered.
Id also say largely depends on car colour. Mine is black, so id probably prefer a non black edition, so it breaks up the rear a bit, certianly dont fancy paying extra to not even see the diffuser!