Swiss trains are not terribly expensive and the railroad sets the tarriff. Zurich Hbf is a nice place to buy tickets - the clerks are honest and well-informed. I once did a get a special deal on the Cisalpino out of Zurich to Milan on Raileurope - it was $25 for any Cisalpino route into Italy as well as a bunch of discounts for buying in advance in the other direction - so check Raileurope but note that normally they are about 15% higher than the railroad sites or ticket offices. The Swiss Rail site is fine and the Belgian one is the most helpful. But these all should give the same price.
See http://www.sbb.ch/en/
There is currently a Supersaver sale on the Swiss site with very low fares until Sep 15.
http://sparbillette.sbb.ch/home/?lang=4