In numerous cities and towns, at around 80 stations of SBB and private railroads in Switzerland, as well as at many youth hostels and campsites, you can buy a Rent a bike for a few hours or even by the day - partly free of charge against a deposit, partly for a small fee. All you need is an ID card.
Who a bike cheap buy wants, finds at Bike exchanges used bicycles at reasonable prices. Every year, more than a hundred bike fairs take place all over Switzerland. In addition to used bicycles, they also offer bicycle accessories. Around half of the bike fairs are organized by the regional associations of Pro Velo - the national umbrella organization of cyclists in Switzerland. You can also find numerous online bike exchanges on the Internet. Check with your municipality or on the Internet to find out when and where the next bike exchange is taking place in your area.
Also in community newspapers or on bulletin boards, for example in a supermarket, you can often find sales ads for cheap secondhand bikes.