It may well be more, but how do you know that extra won't be covered up front in someway? Not saying it will be but what's the point in complaining without the full facts?
In a previous post I did some calculations based on 350 million that were easily affordable. (It works out around 9% of income based on the likely income pulled in from extra capacity and naming rights) So that figure could increase to around 400 million and still be ok.
As a funding model it's as safe as it gets. I repeat no sane individual is going to rock up and give the club the best part of half a billion for nothing. The next owner may decide to cover the loan and convert into shares though, depending how inflation shrinks the true value and markets increase personal wealth.
It's ok to have an investigative mind on the situation but it's another entirely stuck concentrating on the 1% of what if. It's like me getting up in the morning one day and deciding there is no point in going on as there is a chance an asteroid may hit Earth and wipe us out.
We need this stadium as a club.