Spurs and England striker Kane has enjoyed a remarkable 2017, scoring 56 goals for club and country to become the continent's top marksman.
"He's got this great ability to be in the right place at the right time to score goals," 76-year-old Mullery told BBC Five Live's Sportsweek programme.
"I think [the way] you can always tell when a player has become a great player is, if he doesn't play then you miss him badly, and I think that's happened to Tottenham over a period of time now that, if Harry Kane wasn't playing, everybody would think: 'who's going to score the goals?'.
"And the reliability goes on somebody else but with Harry Kane you know every time he gets anywhere near the goal, he can score.
"If you double that number up to £150 million, forget it. That's half the price he's worth because he is now the top player in European football."