Viery
Well, you can buy it for 29.- without a half fare travelcard or a Swiss Half Fare Card (the latter being probably more appropriate for you). But you’re not allowed to use it on the travel date without some valid half fare card!
Also, the Saver Day Passes prices are dynamic. Those for 29.- are usually already sold out within a couple of hours after being released at midnight CET six months before the travel date. Right now, those for July 20th are already 34.- (half fare).