Hazard has a year left on his contract, and isn't going to sign a new one. Griezmann has a RC. Both players have informed their clubs they want to leave, and the clubs' hands are tied. Oh, and also, Joao Felix is young, hasn't made any formal request to leave, Benfica are uner no obligation to sell, and are insisting on his RC, which is absurdly high to ensure that very few clubs even try.
These players are costing crazy high, because they are talented, already really good and their clubs are not really interested in selling. Age matters. Next year, Sancho may have a horrible season, and see his price drop down. Or may have a stormer, and see his valuation increase more. Comparing apples and oranges here - price depends more on just quality. RC, Time on contract all matters.
Oh, and if we are losing DDG, and I hate the fact that we potentially may, we should be going all in for either Donnarruma or Oblak.