He also says Sir Alex Ferguson's decision to sell the player could not be judged until the start of the season.
But United midfielder Darron Gibson has claimed that Ronaldo's departure will not be mourned by his Old Trafford team-mates.
ibson said: "You could see it coming. He wasn't happy at United over the last few games and you could see that he was looking to move on.
"But we've got a great squad and I don't think we'll miss him. There are a few that can step in and do just as well as he did so I don't believe he will be missed."
Ronaldo, 24, is expected to return from his holiday in the United States this weekend before flying to Madrid on Monday to undergo a medical and discuss personal terms with Real.
United, who yesterday secured a £37.5 million five-year partnership with Chinese electronics company Aigo, will bank a world-record fee for Ronaldo when he completes his move to Spain.
But Old Trafford director Charlton claims that the £80 million figure merely symbolises the tightening grip of finances on football.
Charlton said: "It's a lot of money. It's crazy really, but if you want to be in the race, you have to pay the price. It seems sometimes a little bit vulgar.
"Nevertheless, that is business, I'm afraid. We have responsibilities to our company and to all the fans that support Manchester United and it was decided that Ronaldo could go.
"There is a little bit soul-searching because you never know if you've made the right decision until the start of the season. It's an enormous amount, though, and we will make sure we will use it properly and our club will be better for it."
Charlton, who made 758 appearances for United, has warned Ronaldo that he may regret his decision to leave Old Trafford for Real.
He said: "I suppose, in time, he will reflect, and say that the best time he ever had in football was when he was at Manchester United. It was better for him and it was fantastic for the club.
"But we have no divine rights. We talked him out of it for one year but he's gone and we move on. If he leaves us, it's with our blessing."
Lyon president Jean-Michel Aulas has warned United that £25 million-rated forward Karim Benzema is only likely to leave the French club for Real Madrid.