"It's a fantastic fee," the 22-year-old said. "It puts a new value on Ronaldo.
"We are talking about an excellent player, so I think it (the fee) is fair."
Ronaldo is the FIFA World Player of the Year and has won numerous titles with Manchester United.
"He deserves everything that has happened to him considering what he has accomplished in recent years," said Nani, who will remain a team-mate of Ronaldo's in Portugal's national side.
"Real Madrid is a great club and I wish him luck."
Manchester United have proved time and again that they can overcome the loss of key players, although Ronaldo will be hard to replace.
"We will have to rely on other stars," he said.