This is an interesting read.
https://www.london.edu/faculty-and-research/lbsr/why-is-manchester-united-so-successful
The world transfer fee for a single player was 8 million. If this "spree" included Feguson spending the same amount for 5 players to rebuild their failing squad, then I'm not sure how this doesn't illustrate that the comparison between them back then and them now is flawed.
Moreover, the spine of their 90s teams wasn't expensive.