$20k can't get you that many PhD. Even PhD students, who's nominal salary is maybe $3-5k a month, effectively costs double that because of school overhead and other stuff.
Would definitely rather have a single postdoc in a relevant STEM subject from somewhere like Imperial for less than half the overall cost than an LLM all in though. And I say that despite seeing the quality of the memes they produce with generative AI....
Do they really get paid that much these days?
But it is true that in Europe, Switzerland PhDs (and professors too) make most. Not just ETH/EPFL as well. UZH (Uni Zurich) has salaries of 50K CHF per year for PhD candidates (with increments every year) -- that's almost 60K USD by your fourth year. This is also true for other universities. And while Zürich is expensive, it is not _that_ expensive.
You can reliably assume that PhD wages must eventually converge to the rent of a studio apartment nearby + a little bit (which may or may not be enough to cover all other expenses. Going into debt is common.)
Computer science is rate 5, so 73kCHF the first year, 78kCHF the second, then 83kCHF onwards.
But you are not getting a PhD worker for 20K with "AI", that's just marketing.