Used to be that even if you were a GTA at my school you still had to pay tuition, and you HAD to take a certain number of credit hours a semester to hold a GTAship.
Not anymore! (With caveats, of course, but they don't apply to me.)
So my salary just about doubled; now I'm only $6k away from making a 'living wage' for my area. (Good thing I didn't go to grad school to make money.)