We've become so blase over transfer fees and when you've sold Maguire for £80m it's easy to understand why you'd think £50m for Tielemans is cheap but I'm really not sure it is.
£50m is right at the top end of what I think Tielemans is worth, certainly to a club like Liverpool. If we signed him, at least in short to medium term, he'd be nothing more than another midfield option and possible wouldn't start the biggest games if all of Fabinho, Henderson and Thiago were available. Spending £50m on that sort of player, when there will be comparable players available in France & Germany for half that fee this summer, just doesn't make sense. If you're going to spend £50m+ you'd want somebody that was going to be an obvious upgrade on what you have.
I can understand why Leicester would demand that full £51m (if he has a clause) or more if there's no clause but short of somebody specifically identifying him as the one player they want (like Utd with Maguire) then it's difficult to see who will pay £50m+ for him. There's very little money outside the PL and with a lot of European clubs desperate for cash, there's going to be some bargains to be had.