Judging the actual value of a player is extremely complex, not least an outlier like Cristiano Ronaldo.
When Ronaldo signed for Real Madrid, he cost them an eye-watering £80 million and became the most expensive footballer in history.
He arrived at Manchester United a raw talent and left Old Trafford as the finished item.
Or so we thought.
Since arriving at Real Madrid, the Portuguese star has managed to improve in almost every way.
He even dives less. Why hit the deck when he can just run past his opponent?
Ronaldo has grown stronger, faster, and even though it seemed impossible, even more confident.
He has pushed the boundaries for what the pinnacle of the modern footballer should be.
Lionel Messi plays in a more old fashioned, classical style, not to say that it makes him any better or worse.
Which is the better player is a debate for a different day and no doubt one that will rage on in years and decades to come.
His improvement at Real Madrid would certainly have added millions to his market value, although at 29 he has reached his peak.
It's unlikely that the Ronaldo we see next season will be better than the one we have this year, although he could maintain this level.
He has 11 goals in 10 La Liga and Champions League matches in 2014, form that nobody can criticise.
His strikes against Schalke on Tuesday night took him level with Ferenc Puskas on 242 goals for Real Madrid.
There would be a huge drop-off in resale value if the team that bought Ronaldo decided to move him on.
Presumably, if (theoretically) he was sold this summer, he would stay at his next club for at least two years.
However, physically he is so impressive that he may enjoy a slow decent rather than the rapid decline players like Dimitar Berbatov showed.
Madrid would also have to take into consideration the commercial losses they would suffer.
They are arguably the biggest club brand in the world and would publicly consider losing Ronaldo's image just a drop in the ocean of their wealth.
But the star is one of the most marketable faces and names in football history and losing him would have an impact on the amount of money they would make from sponsors.
It's important to use recent transfer deals as a marker to judge how much Ronaldo is worth.
Comparing his form in 2014 to Ronaldo's, you will find that the Welshman has six goals in 12 Champions League and La Liga matches.
That's not necessarily a bad total, but it shows you how far Ronaldo is ahead of him at the moment.
Then again, Bale is only 24 years old and his best years lie ahead of him.
The most likely scenario for Ronaldo leaving Real Madrid was if Manchester United bought him last summer.
However, even though David Moyes (or whoever else is in charge by June) will have plenty of money to spend, Ronaldo is not likely to move to a team not competing in the Champions League.
This means that Real Madrid would also have to add money to his value to make sure they accounted for the damage he could cause them if he was drawn against them in that competition.
Madrid's goal for many years has been "La Decima," the 10th European Cup.
Imagine the scenes if Ronaldo was allowed to sign for another side and he prevented them from winning it.
His contract also expires in 2018, which is some way off and wouldn't have a negative impact on his value.
Bearing all this in mind, Ronaldo is worth between £135-145 million.
Something that only a handful of sides would be able to stump up, and it's extremely unlikely that any of them will.