Well, the unadjusted cost of the Starr investigation was $82mill, so Mueller is being pretty efficient in spending. Regardless of what you think about the mandate, cost isn't the issue.
Our government spends more than that to kill roaches on our military bases.
Of course many of those roaches are probably smarter than Trump's campaign officials...
$17M? Is this going to cut into Trump's budget for travelling to Mar-A-Lago to hide and play golf? I sure hope not.