Only PhDs are paid. I think the salary scale starts at around 51,000 CHF. That's a lot for other countries but it isn't for Switzerland. The exact amount is public knowledge and you can find it if you look. It is slightly higher for ETHZ, but not much.

Bachelors and masters pay fees according to: https://www.epfl.ch/education/studies/en/rules-and-procedure... or https://ethz.ch/en/studies/financial/tuition-fees.html

Tuition is definitely not free, but also not extortionate.