If we’re going for potential then I think what people mean is Lukaku when he first joined / signed potential rather than Lookman / Vlasic potential.
If they do mean the former then, as you say, you’re looking at £35-40m in today’s prices.
Then there’s the fight on for them if a CL team also has an interest.
If it’s the latter, who are cheaper and easier to sign, we already have those types here.
Yep, if Walcott was 18 and coming through at Southampton now he'd be on his way to Liverpool for £75m.