It's United, United can never sign a player at that age that's coming from somewhere in Europe for less than 30m, on top of that. There's clubs interested, no buyout clause. You have Dortmund, Leipzig, Chelsea, United, PSG I think 40m is the minimum you'd pay honestly and even if you are buying potential you are paying more as a PL club, and forward position.
Chelsea just signed a 18 year old Villa defender for 20m. This is not 2017-2018 anymore, young prospects go for a lot of money these days. Sesko is a great prospect and he's 19. For that position there's what? Haaland, Nunez had a good year and look at what Liverpool paid. Not saying Sesko is anywhere near the same level right now but Nunez is 23, Haaland is 22. Sesko only just turned 19.
Would we sign a player like Greenwood for the same money if he didn't do what he did right? we'd probably be paying 70m, so I think it's genuinely warranted. He's in the mould of a Lewandowski, has all the attributes to be a top striker but of course its not certain but you take that risk.