In the 80s it was "market rate." In engineering my TA position paid $14k a year + free tuition. The money was a little less than half of what I could earn in industry at the time, but free tuition (and an actual job offer instead of an open-ended job hunt) made it attractive enough to keep me around for a Master's degree. They offered me a PhD, with a raise to $18k/yr for the TA-ship, again right at 1/2 of what my MS was worth on the open market - I had had enough of academia, no thanks. Only took 6 weeks to find a "real" job.

Over in the business school, they had a lot more students competing for the TA positions, over there they paid $4k per year + free tuition. Seems that more business students come from families where their expenses continue to be paid by family through 6+ years of college.

I co-taught a lab with one other TA vs about 15 students, and we helped grade papers for the lecture class... could we have been replaced with AI? Maybe, but would AI stand over your shoulder and ask you "what happens when I pull this wire out of your breadboard?" then talk you through the reasons why your quick and dirty design may work in the lab, but it doesn't meet design specifications and will likely fail in real-world use where it's used millions of times a minute for years instead of 3 or 4 times for a bench test - pulling that wire is the same as your design being completely incorrect, and yet: your bench tests are all still passing... think about that.