I think similarly to Lookman (although further along clearly) he has a way to go. I don't think he's a slam dunk that numbers like 100 million should ever be considered in the near term. Remember how much we sold Lukaku (although yes, pre-Neymar deal) for and he was regularly scoring high numbers every season.
If he leaves Man United (I think if Mourinho leaves that becomes less likely) he'd want to go somewhere to play as a striker I'd imagine. To that end, he's still a bit of a work in progress and if we'd need someone to hold the ball up in that position...that's not exactly his strength. Likewise his finishing is hit and miss, reminds me a little of Walcott actually in that he can get on a good scoring run but he can miss some good chances too you'd think he'd be scoring. Yes he scored for England (hence this story/talking point to begin with) but he also missed like 3 great chances in the last match...probably the difference in losing and getting a draw in that game.
So while I'd take a chance on him, it would be taking a chance to a degree and I'd certainly don't think he'd be worth paying much over 50 million for...and I can't imagine many other teams would pay over that either.
If he was looking to leave, I doubt there would be many other clubs who'd give him the same amount of playing time if that is what he's after, unless he went on loan to a bottom half PL side. So it would be a good fit.