It is likely that West Ham will have to cough up about £5 million for Barnes. Barnes had a terrific campaign last season, helping Derby gain promotion to the Premier League, but this season due to injury he hasn't played as many games as he or Derby would of liked. Barnes has made 65 appearances for the club scoring 9 goals in those games.
I think this would be a good signing for the Hammers because Barnes clearly has a big future ahead of him. I think Derby are right to look at letting Barnes leave because if they are to get relegated, which lets face it will probably happen, his value is bound to decrease. Barnes is also said to be keen on the move so I expect a deal to go through in january.