A young Ronaldo would not be an €80m player, just like a young Rooney wouldn't; you can double that if not more, so it's not really a fitting comparison. €80m is £67m? That doesn't even get you someone like Rice's left leg, let alone a top-potential talent of the ages' interest. Tchouameni just went to Madrid for €100m, a club with more power and leverage than anyone else on the planet, and he's 'only' a defensive midfielder.
Antony is overvalued as he's not in those tiers of 'most certain to be world class' talent that people expect once the numbers go above a certain amount, but you only have to observe the market, and then our predicament, to see why things are this way for us.