In this phase, it is a difficult choice for PSG to let go of its players. however, if Mbappe is adamant about sticking to his statement by not extending his contract. that means, PSG will look for a strong candidate club that wants the services of this player from France. but are there many clubs willing to bring in Mbappe with a fantastic salary, the only realistic team is Madrid. Madrid can bring in Mbappe, even the problem of salary is not a big problem for them it seems. in particular, currently Don Carlo has only signed Joselu "as far as I know". thus, it is possible that Madrid will propose to Mbappe even though the President of Madrid previously stated that he would not bring in another striker. but, anything can happen.
Salary will not be a problem for Real Madrid and so far they have never thought about this problem because Real Madrid has the ability to deal with big salary problems. For PSG it will be a big loss when this summer's transfer market does not sell Mbappe, because of the player's statement that he will not renew his contract again. If after the transfer market closes and Real Madrid don't manage to bring in a quality striker then I'm sure they will have a hard time competing especially in the Champions League.
Harry Kane could also be Real Madrid's choice if Mbappe is not released by PSG, but again as you are talking about Tottenham set a pretty fantastic price and Real Madrid are not alone in pursuing the player's signature because Bayern Munich are reportedly getting closer to Harry Kane