As far as I can ascertain, the main seller for this wine in the UK is/was the Co-Operative, with prices varying between £8 and £9 a bottle, which would put the retail value of a case of 12 at around £100.
So full retail price is circa £100 for a case of 12. Value sold privately? Probably somewhere between £60 and £80 (depending on how close the buyer is to Woking, and how willing they are to buy a full case - rather than a single bottle, initially, to try - with no knowledge of how it has been stored).