[masterofmasters]

It's not a ton, but he could also get a summer salary if he has grants for it (netting 33% more salary) and do some consulting on the side.

Also on the whole we should take into account that professors didn't have to pay for grad school unlike medicine / business and instead got paid for it.

[plg]

true. As a grad student I did get a salary. You know what it was? $11,000 per year...