Talking about the money, Messi had taken a pay-cut before to remain at the club, I'm confident he can make that sacrifice again for Barcelona been fully aware of the conditions of the club.
When Messi agreed to a pay cut then to remain in Barcelona, he still had some years to play in soccer than he has now. Agreeing to a low pay just because he wants to return back to Spain will be a bad economic decision.
Follow the Money Lionel, there is nothing else for you to proof.