When talking about a young player and there transfer value, you have to remember there will be an up front fee, probably around 6-8mil in this case, then you have add-ons for appearances, goals, international caps and so on.
I think if you take all this into account then the potential transfer value of any young player, Zaha or otherwise will be over £10mil.
£20mil for someone who is a U21 international and playing in the Championship is mad but unfortunately thats the market.
We paid £20mil for Henderson who I think maybe had one full cap so whats the difference?