I am inclined to agree with that too. In no way pouring cold water on what is overall a great thing for us, and certainly no expert, but it does seem on the more modest scale of outlay if that's the total, even excluding comparisons with London. The financing model suggests to me that we would have room for a bit more oomph and ambition.
He also made a good point about Moshiri putting in 50m or so, if that was the difference between 50k and 60k total capacity it would mean a lot.
The devil is in the detail. I would expect total construction cost to rise over the duration of the build anyway, but its important that what gets built stands the test of time and doesn't just blend into something average, bland, uninspiring.
To me we need 60k + best in class build and design. If the budget is 300m then we will have to compromise on one or both of those aims.