I'm using a pre-paid Lycamobile since the time of my arrival: ordered it even before the arrival to my assumed address and registered it just with a passport and a registration confirmation (it's provided immediately) in a nearby Kkiosk. I'm buying M-bundles on a monthly basis (used to be 19 CHF, starting this month 24 CHF).
Sometimes I leave abroad for a few weeks using my second SIM card and if it's exactly when my current bundle expires I just don't prolong it

Not a big win, but something.
There're cheaper contract-based providers though, I haven't tried them.