To expand on this, IIRC postdocs cost professors about the same, but have double the salary, only because the school isn't taking the "tuition" cut. Of course,

To expand on this, IIRC postdocs cost professors about the same, but have double the salary, only because the school isn't taking the "tuition" cut. Of course, the incoming grant money to pay for the postdoc is still "taxed" at 50% by the university. So the lowly PhD student is probably only seeing 25% of what they're costing the government.