I am not trying to compare the quality of the two players as Casemiro is head and shoulders more decorated as a player but when Thiago Alcantara was signed, he cost at least £50 million less in transfer fees and around £125,000 less in weekly wages (I didn't bother double-checking). That's a lot of money if you factor in the entire length of the contract. Also, Thiago was 1-2 years younger.
The comparison between these players makes zero sense to me. Liverpool, the penny-pinchers, and United, the extravagant spenders, cannot be compared.
As someone rightly said, it is the Glazers' money, so why bother?