This 400K thing is silly.
It's a big signing fee + a wage a Manchester United star can expect, that probably equates to 400k a week, but that is the nature of a transfer in Sanchez's situation.
Sanchez: 400K x 3 years = 62m
Any other player: 300K x 3 years = 47m
The difference between the two amounts is that for a normal player funds would be given to the selling team, thanks to Sanchez's situation the 15m difference is a signing bonus. This is no different to any other sort of numbers you'd expect in 2018.
I don't know why people are running around trying to pretend this is some outrageous figure - it's a standard transfer being sold by the media as something else.