Bern to Paris and the swiss half fare card

Hello,
Can anyone please help me as to where to buy cheap train ticket between Bern to Paris ticket for Oct 12 at around 7 to 7:40 am departure one way? I tried using the raileurope webstie but its quite expensive? I also tried www.sbb.chwebsite but prices are more expensive than the prices on the raileurope website. Are there any tricks that I miss in searching? I am also interested in this particular time Bern dep 7:29, Paris arr 12:18, I can't check the price at sbb.ch. It tells me that the site is under maintenance and cannot book international route but when I tried other route from Bern to Paris, the prices are reflected. Please help

I'm also planning to get the Swiss half fare card. Do you guys think its worth it? This is my itinerary

Day 1 Arrive Bern from Milan in the afternoon -- Bern
Day 2 - Bern
Dy 3 - day trip to Lucerne and back
Day4 - Bern to Interlaken, climb Jungfaujoch
Day5 - Interlaken to Bern, Bern to Paris

Can I use this for my Bern to Paris trip? Will I get discount? Should I purchase this early or can I purchase this at Bern railway station upon arrival?

I am so confused with all the offerings. Any form of help is much appreciated. Thanks!

Thanks Arno! Country of residence is Philippines. I have one some more questions if you don't mind. Can i get my Swiss half fare card at Bern station? Do i need to prebook train ticket from Bern to Lucerne and back as well as the route Interlaken West to Bern before hand or can I just get them on the day of departure? If I have the Swiss half fare card, are all the modes of transportation in Bern and Lucern half fare as well? Even the Bern transportation multi day pass? Appreciate all the help. Thanks in advance.