Spending a ton of money for a player is not really a priority for many teams right now because they didn't made a good profit (and most of them lost a great deal) because of the pandemic. It means transfers like Mbappe is a pipe dream by the fans right now, not that it can't be done, it could have been done right now as we speak if we never had pandemic, but because of lack of funding it is harder right now and that is why I do not think that it could be done that easily.
This is why I believe there is a good chance no team makes any transfers above 100+ million levels (which mbappe would have been very easily), there is an exception for Chelsea which can buy Haaland if Dortmund agrees to sell, but that is only because they are the team that won the most, 4th in premier league, finalist in fa cup, winner of ucl, all of those equals a ton of money.
I don't think it will be a lump sum, especially given the current difficult coronavirus times and falling revenues from the TV market. Therefore, the deal can be drawn up with tranches for several years, and other players can also be included in the deal. By the way, I think that Real Madrid would be happy to buy Mbappe for 100 million euros, because this is a very good price for a player, given his playing level and marketing potential. Moreover, as far as I understand, UEFA has decided to allow Real Madrid to play in the Champions League, which is important for the club financially.