Qwiss Isak is, but he isn't for sale and if he was he'd cost £150m. This is why teams pay a premium for PL established players, they come in and make an impact straight away. Part of why Madueke is probably more expensive is he comes in and is ready to go and the coach and analysts have a large enough sample size in the PL to see how he would perform.
With Sancho I think a lot of it is down to mentality, he's definitely got the ability but mentally is not where he needs to be. He may suffer from some mental illness conditions (depression etc) or some of it could be he isn't as driven as he needs to be. I think Klaus showed in another thread a video about Gyokeres, even if I don't think his skillset is elite his mentality without a doubt is elite. Things like that will go a very long way and could make a success out of a player, we've seen incredibly talented players like Ben Arfa for example, this guy could have been as good as anyone but a completely shit attitude meant he never made it. Gyokeres being so focussed is definitely a massive positive and carries a lot of weight.
Wirtz might be a flop but from what I've seen, he has a strong mentality and elite skillset so the risk is less.