[masonic]

  The Big Dig in Boston was originally estimated to cost $8 billion. 

No, $6 billion in 2006 dollars ($2.8 billion in 1982) per Wikipedia.

  It ultimately ended up costing $22 billion

$24 billion, according to the Boston Globe (10 July 2012), yielding a nice, round 300% in overruns.

  At the end of the day? It was an awesome project. 

Seriously! It's so nice when your "$6 billion" project gets $8.55 million in Federal funds that the locals don't even have to pay for.

The Big Dig cost almost triple what the entire Panama Canal project did (adjusted for inflation). There's nothing to be proud of there.

[cow_patty]

The difference between the $8.5M in Federal funds, and the $24B that the locals had to pay, is about $24B.

[masonic]

s/$8.55 million/$8.55 billion/

[thisisweirdok]

If you want to put the Panama Canal through Boston it's going to cost astronomically more than $24bn — the logistics (not to mention the requirements and processes of the time period) are entirely different.

[BubRoss]

How is that at all relevant?

[sporkland]

The grandparent poster compared the cost of the big dig to the cost of the panama canal to in an attempt to show that the big dig was overly expensive.

This parent poster is pointing out the fallacy by hypothesizing that the Panama canal in Boston would be way more expensive than the Panama canal in Panama, thereby showing the error in the grandparent post's reasoning.