So far, PSG aren't setting a high price on Mbappe, they've fully insisted that Mbappe will not be sold under any circumstance, and I believe PSG can be very adamant when it comes to keep their star players (Verratti transfer saga to Barcelona still fresh in mind).
So, I guess Kylian Mbappe would either have to force a move or see out another year from his contract at Paris, at least.
I think PSG will not let Mbappe go anywhere. They've yet won the Champions League and Mbappe is a core player in their plan. He is young and can contribute more for PSG. PSG can win Champions League and their strength in next few seasons will be even bigger than Real Madrid.
If the desire of Mbappe is Champions League, he would keep playing for PSG. And if he wins Champions League with PSG, he would not go anywhere. Stay in Parc de Princes and become a legend.
Wijnaldum after being heavily linked with Barcelona have opted to join PSG instead.
Wijnaldum won't have a secure position in Barcelona if Busquet still has a solid position in the squad. The traditional tactic of Barcelona make energetic midfielders have difficulty to adapt to. They have Arturo Vidal in the past and I don't see they used him so well.
It can be one of reasons that Wijanldum don't want to join Barcelona, besides the higher salary from PSG.