PhD candidates in the US usually get somewhere between $25K and $50K stipend, also some level of benefits (typically health care). Sometimes there is a tuition waiver (student does not need to pay grad program tuition).

In my case I was making $32K/year with a tuition waiver and health benefits around ~2000, in SF, which was barely enough to rent a shared apartment and eat food. The only way I could rationalize it is that I was maximizing my future freedom (job choice).

Yeah, I distinctionly remember a postdoc I knew who was irrationally excited to move to a role where they were going to get paid $35k, in 2010s money, and they were damn excited about it. And they were moving to a high cost of living area (from a high cost of living area). I was utterly flabbergasted because they were very smart, very technical and should have been earning 5-10x that. I feel like they didn't know what they were worth and academia had utterly failed to teach them that.

I don't know how they paid any of their accumulated (I assume) student debt, let alone had an even decent standard of living.

Wait, some PhD candidates are being paid near minimum wage and are still paying their university to do work for their university?

That just sounds like indentured servitude with extra steps.