What's the most expensive transfer ever?
It seems obvious: Paris Saint-Germain paid the €222 million release clause to acquire Neymar from Barcelona. The only other player who has come close to that was another player acquired by PSG the same year: Kylian Mbappé, for €180 million, from Monaco. No one else has moved for even €150 million.
But €50 million in 2025 is a lot different from €100 million in 2015, and money spent by PSG is a lot different from money spent by, say, Marseille or Mallorca.