Half fare card is CHF 185 for the first year or CHF 165 for every subsequent year (CHF 120 / CHF 100 if you're 16-26).
For anyone planning to spend any amount of time in Switzerland and using PT, it is well worth considering. It does exactly what it says, you only pay half.
So assuming you travel from Zurich to Bern (CHF 51 -> CHF 26, you safe CHF 25), it's worth it after only 8 trips.