I agree 400 million is too expensive for the price of Osimhen. His performance is decreasing this season, his price should be lower than the previous transfer window. Man United probably won't spend 400 million for signing Osimhen, they can get more than 4 star players with that money. Even Saudi clubs won't have the intention to sign Osimhen with 400 million. It is just nonsense to set the price 400 million. 
I'm sure Mbappe and Haaland must be above 200 million if he has a contract with their current clubs. But Mbappe seems to be free agent because his contract expires in PSG. Well, if Napoli sets the price 150 million, I think there is a chance for selling him. Real Madrid, some top teams in EPL, and Saudi clubs are probably interested to negotiate with Napoli.
I think it was just made up by the media by saying 400 million I don't think this will happen for the sale of Osimhen because this player is not his level at that price, it also doesn't make sense and who wants to buy him? If you say this is nonsense then I believe it.I'm sure Mbappe and Haaland must be above 200 million if he has a contract with their current clubs. But Mbappe seems to be free agent because his contract expires in PSG. Well, if Napoli sets the price 150 million, I think there is a chance for selling him. Real Madrid, some top teams in EPL, and Saudi clubs are probably interested to negotiate with Napoli.
Mbappe does have a high value at the moment the contract at 200M is still very possible especially now that Real Madrid is still eyeing him until his contract expires. Let's see how Real Madrid make a special offer to Mbappe.
I don't know if the 150M for Osimhen will go to Chelsea this is just a rumor while Real Madrid will not prioritize the Napoli player, while for the Arab club Osimhen there is no interest there.
This is definitely just a baseless rumor. And this is definitely made by the media, I absolutely agree about that. The media just thought about making up a random number which is high and make some interesting news. Otherwise, I do not think any club is actually going to pay 400 million for him. Don't get me wrong, he is definitely a good player. And he has a lot of capability. But I absolutely do not think that he is anything worth 400 million. I do not think there is any player in the world right now who is worth 400 million. Maybe if Lionel Messi was younger and in his prime right now, or maybe Cristiano Ronaldo in his prime at this moment, could have actually pulled off a number like that. But there is no player in world football right now to actually deserve that much money as a transfer fee.
Mbappe and Osimhem will continue to be the hottest properties in every transfer window, because they are young, talented and consistently score goals, and can certainly increase the bargaining value of a club in the hunt for trophies in all competitions in which they participate. Apart from that, the real challenge is that there are many interested clubs, especially if clubs from the SPL enter the competition, they can set a transfer record as easily as turning the palm of their hand.
We can refer to the market value of the two players.
Mbappe : https://www.transfermarkt.co.id/kylian-mbappe/marktwertverlauf/spieler/342229
Osimhen : https://www.transfermarkt.co.id/victor-osimhen/marktwertverlauf/spieler/401923
I never use market value as a benchmark to know how big or low the suitable price for the price is. I meant the price being determined by the club itself and it's not coming from the market value. Market value was only telling you about worthy price for the player based on the various factors determined from the providers. The team itself has various considerations before they will be trying to give how much price is worthy for their players.
Look at how osimhen's release clause has been going up and down like what was demanded by napoli's president. Think about that. Market value was not an accurate benchmark. It's baseless and we don't even know what factor that was infuencing the price provided by the author. I rather than believe with the price that was officially announced by the team itself rather than use market value from transfrmarket as bench mark to determine that.
Think about that. I think that we shall wait for the official announcement regarding the price of player. Even mbappe has determined his own price which was 135 millions.