Why would Barca sell messi at any price.
There is no replacement for messi even with all the money in the world.
Clubs like Barca and Real Madrid are not trying to profit off of player sales, they are after prestige.
He is the clubs legend and greatest player.
Barca is not owned by a individual it is basically owned by the season ticket holders who appoint a president. Any one who even thinks about selling messi would be crucified before it happened.
Same goes for a player like Bale, they are simply not plausible, that is why we are after someone like de bruyne.