Swisscom natel easy Sim is chf 20 with chf 19 credit. Acceptably fast internet (1mbps - worked ok for me) is chf 2 per day.

I tried to get this at the Swisscom shop at the ZRH airport train station in August but they had completely run out of SIM cards! We ended up in Weggis which had no Swisscom shop, but I realized they sell them (and perhaps others) at post offices.

Worked out great for some email, Google maps, SBB.ch app, posting the odd photo, etc. I wouldn't want to use it for a lot of video or tethering, but we had free wifi where we stayed and many cafes had it too.