"(Just imagine the recriminations if any public sector agency ever blew through its budget by a similar margin.)"

Geez, I expected better effort and intellectual honesty from a renowned economist like Sanford.  Public sector examples are easy to find.  Muskrat Falls is more than 50% over budget.  Ontario's eHealth project.  Just about any military procurement project.  

A cost overrun for a major, capital-intensive project is pretty much expected.  The Sydney Opera House was ten years over-due and cost 14x the original budget.  (Oh those Ozzies!)  Montreal's Olympic Stadium was budgeted at $134m but cost $264m by the time it opened. A 50% cost over-run seems tame in comparison.

Just imagine if...indeed.   You undermined your credibility with this gratuitous (but unfounded) shot.