You cant possibly discount the wage bill completely in the modern game with Bosman signings and pre-contracts, United are arguably the most famous club in world football(or in the top 3 at least) so will guarantee the attention of any player they are interested in and will offer the wages to make them a very attractive prospect for the worlds best. Any club who haven't been on the ball with their top assets contract details open themselves up to losing players to united with little or no compensation, meaning its not purely about the transfer fees involved.