The Welsh forward, who recently landed a PFA awards double by being named Player and Young Player of the Year, continues to be heavily linked with a summer move away from White Hart Lane.
Spurs are understandably reluctant to part with their most prized asset, with Bale having helped to fire them into contention for a top-four finish in the Premier League.
They would demand a sizeable fee if a deal were to be done, but Zidane does not see that being an issue for the sides reported to be leading the hunt for Bale's signature.
The former World Player of the Year said: "After the season he has just had - and still being so young, of course - Gareth Bale is going to be one of the most expensive players in the world if he decides to move.
"Tottenham could demand £40m, £50m, maybe even £60m for him. It is a lot of money, but there are maybe three or four teams in the world that can pay that sort of transfer fee, and it won't put them off.
"A player like Bale can be the difference between a big club winning the league or the Champions League.
"They would be getting the best player in Europe this season - and he is at an age where he can still play at the top for another 10 years."
Bale has attempted to play down the speculation regarding his future, saying: "I just take no notice, it's all speculation, I can't do anything about it.
"I just concentrate on my football and play as well as I can and do my best for the team."
He is, however, considered to be a summer target for Real, their Primera Liga rivals Barcelona, German champions Bayern Munich and wealthy Ligue 1 outfit Paris St Germain.