Players who play consistently for England are always quite marketable so that increases their price, plus he will count as a home grown player (or whatever it is), still quite young too. He is definitely a good player and transfer fees have gone wild in the last few years. Is £70 million even a lot of money any more.
Plus Premier League clubs are loaded and everyone knows it so prices always go up.
Wan Bisakka (who is very good) has gone for about £50 million so on that evidence you'd have to say Maguire is worth more.
£25 million isn't worth what it was 5 years ago.