Sancho's rumoured 25 million euros fee isn't that huge honestly. The real problem is his salary... Why?
Because he makes 7.8 million pounds (~9.2 million euros) a year at Manchester United. Chelsea didn't even pay his full salary during their loan contract.
Is Napoli or Juventus keen on paying this much money per year to him?

I don't know whether he is keen on taking a pay cut.
25 milllion for Sancho in my opinion is a good price, the issue now is his wages a whopping 300,000 is what sancho earns. This wage has been the troubling issue with getting a deal through for him and Manchester United are bent on relieving themselves of that wage burden, the only way to get a deal quickly is to accept a pay cut but until now that decision has not been made.