Here you have the information you need to travel the route of the Glacier Express without paying extra.
https://www.swissactivities.com/en-ch/panoramic-trains-in-switzerland/
If you need more info, I'll try to help you.
Very much yes.
The Glacier Express (and the Bernina Express) is a special service for tourists.
There are totally normal trains (without special catering etc.) along the entire route from Zermatt to Brig to Andermatt to Disentis to Chur to St Moritz (and return) which run at approximately 1 hour intervals. They cover the route in several sections but each connects to the next very well.
I have covered most of the route with an 8 day Swiss Pass in the last week, and over the previous 40 plus years with various Swiss tickets that were better value at the time.
My only sadness is that on most normal trains it is now impossible to open windows to hang out and take photographs. That has been the case with the GEX for over 20 years.
Just go, just do it.
Advice is to use some other site to search. Like that of Swiss railways, https://sbb.ch , In this case I almost advice not to look at the site of the railway in question, https://rhb.ch , as they try hard to convince tourists to take the specially priced touristy trains…
And yes, there are lots of other trains that run the exact same route, with the exact same views, without any additional fees. Once an hour or so. When you use such you can stop at some station for a short walk and continue in one or two hours, for instance. Not so if you insist on traveling in the special price ”Express” train and just have to sit therr at your expensive seat.