Bale, who left Tottenham earlier this month, scored on his Real debut against Villarreal but missed a La Liga contest against Getafe at the weekend due to an injury.
"Bale has come cheaply," Perez is quoted as saying by Cadena SER radio.
"Signing the best players out there is Madrid's philosophy and Bale was the best available player on the market this summer. We had been following him for two years.
"Tottenham did not want to sell. We learned that Manchester United had made an offer and we made one ourselves.
Perez added of Bale: "Since childhood he had had the dream of playing for Real Madrid and he asked us to make it possible for him to come."
Bale was named the Professional Football Association Players' Player of the Year, the Football Writer's Association Player of the Year and Young Player of the Year last season.