Well, consider this.
We previously bought Pogba, as a starter for £89M. That was when players were cheap (don't laugh). Had we bought him 2 years later, maybe we'd have paid £130m or slightly higher.
Matic arrived a year before Fred, for £40M and he is quite old, so his resale value is low.
A year later, we paid £50M for Fred, who is a young guy, good enough to play in the first team, but not a starter.
If you want to buy a CM, who can start games regularly, then you will need to pay around the £70M mark, in today's market.
I'm not sure about rival teams, and quite frankly I don't care, but £50M for Fred - a squad player who is still young and needs time to adapt, is about right. And let's not forget that Woodward wanted to get a Brazilian, to target the south American market.