Exactly. Cost vs value.PSG is owned by people with so much money that £200m has no consequence to them. I think I'm right in saying that £200m was the amount needed to trigger a release clause so that is what they paid. I dare say if it had been £250m, they'd have paid that also.
I know you've been around the block long enough to know that price paid, value to the club and player worth are often entirely separate entities. Compare and contrast what we paid for Gary Hart and CMS compared with the relative contributions they made to the club. Or even someone like Peter Ward at Brighton or Zaha at Palace. Both players are respective club legends and worth their weight in gold to both clubs but both went for big money transfers and flopped.
I'm not sure there's any science at all to player transfer values, it's a bit like the housing market. It is what people are willing to pay and no more than that. It's all very subjective and Neymar went for such a huge amount that it would be unwise to use it as any kind of measure, it's just too much of an outlier.