players like neymar, mbappé, ronaldo's ,messi's, etc...just real madrid or barcelona can afford him
even united or liverpool don't buy world class players from other world class teams (I mean, Bayern, Real or Barça)
only if they wan't to sell him (Varane, for example)
United
Pogba (Juventus)
Maguire (Leicester)
Sancho (Dortmund)
Lukaku (Everton)
Di Maria (Real, but they want to sell him)
Fernandes (SCP)
Martial (Monaco)
Fred (Shakthar)
Bissaka (Palace)
Ferdinand (Leeds)
Mata (Chelsea but Mou want to sell him)
Matic (Chelsea)
Mkhitaryan (Dortmund)
Varane (Real - Injury prone)
Van de Beek (Ajax)
Berbatov (Tottenham)
Bailly (villarreal)
Shaw (saints)
https://www.transfermarkt.com/manchester-united/transferrekorde/verein/985/page/2
Only Sanchez (Arsenal) (but he demanded a huge wage), Matic (Chelsea) and Pogba (Juventus) are the only 3 players that United buy from others top teams in "normal" condition
rest of players are from great teams but not world class teams
even liverpool top transfers are alisson (ROMA) and van dijk (Saints) and now darwin (Benfica) and even Keita (Germany)
the only teams that buy with regularity world class players from other world class teams are Real (Ronaldo, Beckham, Kaka, Xabi Alonso, Zidane, etc) and maybe Barça