Ok the steak example is fine, you have to weigh in all the mentioned factors and finally decide if you're willing to buy it for that price. That, for me, is the definition if a product is "worth" it to me.
Same goes for Pogba:
-team needs
-history
-age
-character
-talent
-probability of reaching potential
-work rate
-affect on team chemistry
-sponsor potential
-willing to stay?
+ a thousand more factors to finally come to a value, where you think you'd have a good deal. Always compared to other players in today's market.
So you come to the conclusion that Pogba is worth around 150M to us. We begin the talks at 80M and will stop if Juve won't sell at 150, it's that simple.
We won't bid 200M, because he's NOT WORTH that to our club.
And there are fans who think he's worth even 200 and some who thinks he isn't even worth 100. A matter of opinions and no one is right.
However, I trust Mourinho and Staff more to weight in the factors above than the average caf poster, this is why I'd still be happy if we 'overpaid' a little for him.