The big release clause will of course be a consideration for ancelotti to try to sign Mbappe, I have no doubt that Madrid are a rich team but of course they also won't want to spend a lot of money on just one player, I think madrid main target now is to find a replacement for Benzema remembers his old age, while for midfielders of course currently Madrid still have alternatives because they still have Valverde, Camavinga, Tchouameni and also Ceballos in the midfield, so replacing Kroos and Modric is of course not too difficult for Madrid because they are still there talented young midfielder in their current squad.
Somewhere close to 300 million would be required to get Mbappe, so it’s not only more than what Jesus would cost, but it would be more like 6 Jesus combined. However, you can't put a price tag on a long term success like that.
I keep saying that Real Madrid is just a few players away from being worlds greatest team for at least 10 more years. They already have amazing midfield, and amazing wingers, add Mbappe to that and amazing striker. Only thing left would be the defence and they could get that later on because when you have a team that is filled with such young superstar talents, you don't need to rush into defence, they can go on with whatever they have until they get more money.