I mean you're already, let's face it, describing a completely unrealistic situation where: you know the exact potential a player can get too, MTK Budapest have spent £16M on a player (would never happen), a player at MTK close to getting into the Brazil national team etc etc. Many aspects of this are pretty much pure fantasy but then you complain and want it to match exact real world conditions (when this situation would never occur in real life.)
What is the record transfer for the sale of a player from a Hungarian club? It's probably about £5M.
The highest valued player currently on Tranfermarket in Hungarian football is €6M. So you're doing things that are completely unrealistic to real life (because it's a computer game and yiu can) Juventus are actually acting more realistically. The fact is competition and Europan reputation should affect Transfer values. You're playing in Hungary, your players shouldn't be worth £50M.
Even in real life now, if there was such a layer playing in Hungary, he would maybe go for £20-30M but that's it. The fact is clubs are more circumspect buying from lesser competitions cos they're playing at a lower level so have more to prove yet.
In your example, Juventus should be willing to pay more for that player, that much is fair but don't get mardy about something being unrealistic when you're doing something yourself that is totally unrealistic anyway!