4) Joe Gomez (£3.5m)
Not much was known about the young English defender when Liverpool brought him in from Charlton Athletic in 2015 and the scouts need to be given huge credit for identifying such a promising talent.
Gomez has already played 100 games for the Reds despite only being 23 years of age. He has the potential to go on to be a truly world-class centre-back if he continues on his current trajectory.