If they want him this window when we are unlikely to replace him, then it would have to be for utterly stupid money. It would have to break the world record again in my opinion, because it royally fecks us over going in to this season when things are already a bit bleak around the club, it seems.
Otherwise, if they can wait until next summer, somewhere around what Coutinho went for.
Getting Dembele coming the other way would also help, since we need a RW probably a bit more than a CM. I doubt they, or he, would be up for that though. Getting players in return is a risk if they're not really up for it. You just end up with another player who doesn't want to be here, and likely demotivated by being the makeweight for another player.