1. Luis Figo - Barcelona to Real Madrid, 2000 (€62 million)

A case can be made for El Clasico being the greatest club rivalry to exist in any sport. Not only is it the Catalans vs the Spaniards, but it is also two of the best clubs of all times going against each other for domestic, and European dominance. The match has always been heated and has featured some of the game's greatest names ever.
Due to all these reasons, a move from either team to the other is considered as a taboo, and anyone who dares to do it faces the brunt of millions. As such, when world-class forward Luis Figo moved from Barcelona to Real Madrid, the footballing world was left in a state of shock for years and years.
The move was not only very expensive (it set a world record at the time), it was also extremely controversial. Everyone knew Barcelona fans would be livid at Figo's decision, but no one quite anticipated the level of that anger. Figo became the new focus of the Barcelona–Real Madrid rivalry, with Barcelona fans feeling betrayed by his transfer and turned against him.
He won the Ballon d'Or that year as Madrid player, but the performances which led to him winning the award came mostly in a Barcelona shirt. The Portuguese's arrival also ushered in the "Galacticos" Era, with the best players in the world arriving in Madrid year after year for the next few seasons.
Whenever Figo returned to Camp Nou, the response he got was something no one had ever witnessed before. He was kept away from the corner flag due to the fans behind him, and whenever he got the ball, over 80,000 people booed their lungs out. Whenever he touched the ball, a hail of oranges, cigarette lighters and bottles (the infamous pig’s head was thrown a year later) rained onto the pitch.
"Judas" and "scum" posters were spread across the stadium and barely has one player received this much heat from his former fans in the history of the game.
Also read - Top 5 players who left on a free transfer