Train from Montreux to Zweisimminen to Interlake (via Spiez) - Golden Pass Panoramic?

You don't need to price each leg individually. Putting in Lausanne to Interlaken via Zweisimmen, shows a price of 60 chf (30 if you have a half fare card).
The best deal is likely to be the Half Fare Card for 120 CHF. If the total of full fare tickets exceeds 240 CHF per person, then that will save you money. If you are going to Gimmelwald, you will need to use the cable car and postbus as well as the train from Interlaken to Lauterbrunnen. Factor those in, as well if you plan any other cable car rides like the one to the Schilthorn.
You are seeing a bus because they are doing work on the tracks between Zweisimmen and Boltigen on the dates you want to travel. They have scheduled replacement bus service to get you around the construction.
Also, they only show prices for trains in the next 30 days. Prices will not change, just use the same day of the week in the next 30 days to get a price to show up when you click "Fare/Buy".

Sam,
Thank you for your reply.

I checked on the price of the Half Fare Card which costs 238 chf - so if my train/gondola tickets total 280 chf (as an example).
It would cost me 238 (half fare card) and 140 (50% of the ticket costs. Isn't it less expensive to just buy the tickets without the half fare card since it would cost 378 with the half fare card (140 plus 238)?

Maybe I am misunderstanding how the half fare saver card works?

Doreen

I found a website that offers the half price card for 120 chf.
Your reply was very helpful - thanks again!
Doreen

You can purchase your half fare cards when you arrive. There is no need to purchase in advance unless you are flying in before or after normal business hours of the ticket office. After you have purchased your half fare card, when you want to purchase other tickets and there is no ticket office or it's outside of normal business hours, the machine is fairly easy to use. Select the button for English and the destinations will come up in a list. If you don't see where you want to go, you can type in the name. If you have purchased the half fare card, select the half fare button and you will pay half of the regular fare. You should keep the half fare cards with you as if they check your tickets, you need to have proof that you are entitled to pay half fare. The half fare card is good for almost all trains, busses, boats. If you are taking the bus and there is no machine at the bus stop, you should have coins as the driver will not make change. If you take any boats, there is a ticket office.
When you purchase your train ticket, if you ask, the agent will print an itinerary which will show you which platform to depart from, which platform you will arrive, where you depart again, if there is a bus for part of your route, etc. At the main train stations, there is usually an sbb travel office. If you have many questions, you can go into the travel office and they will have more time to help. You can purchase your train tickets there as well with no additional fees.

Wow!
Your information on buying Swiss train tickets is so very helpful!
Would you happen to know if the cable car / lift tickets are covered by the half fare card and/or the Swiss travel pass. Some of those rides are pricier than the trains. Is there also a super saver pass for a travel companion as mentioned in the RS book?

Thanks for all the invaluable advice!
You guys are the best!!!

Here's a link which you may find helpful. It should be able to guide you further as to which tickets may work best for your trip. If there are specific destinations which you have in mind and you want to be sure you understand the costs, you can research those directly. I've included a link for Jungfrau as an example.

https://www.sbb.ch/en/travelcards-and-tickets/railpasses/new-in-Switzerland.html

http://www.jungfrau.ch/en/tourism/travel-information/tickets-rates/interlaken-ost/fares-for-individual-travellers/