swiss pass

2nd class train travel between those 5 cities should be no more than 120 chf.

When comparing a Swiss Travel Pass or Half Fare Card to buying tickets locally, you should consider any other transportation you'll need within a city and for excursions while there. City trams and buses are relatively cheap, but lake boats are also covered and mountain lift prices can really add up. For instance, see rates for the Jungfraubahn connections around Interlaken. The pass (not the Half-Fare Card) also covers museums.

Look up the prices on www.sbb.ch
In Switzerland, there is no price reduction for advance purchase, and no booking of seats. just buy on the day and get on the next train.