Overpriced. Ticket purchasing is a scam. You buy tickets first, then you have to buy the seats 93 days in advance. Which are all taken by agencies. So you are left with crumbs, and they will not reimburse the cost of the seats if you are not happy with the crummy selection left out. Especially if you are more than 2 passengers.
Beware, one schedule starts on a regular train, you then have to wait an hour for the real deal, then they kick you out, so you have to wait for a regular train. And if late in the season, you will ride the last leg in the dark. Horrible.
Option, travel light, get a Swiss pass, and ride the same route without the high cost. You will have to change train multiple times but heck, you will get there before the Express, which is the slowest train you can find. And mainly, choose your own schedule, avoiding bad weather. Tip: start early.
With the Swiss Pass, no need to buy tickets. Buy the pass online, download the app, just hop in on any train. Also, you can buy a second class pass, and upgrade to first class at 50$ for a whole day.
Controls are random, just show your pass using the app, no connection needed.
Trains run on time, to the minute, so planning is a charm, the spot will tell you on which platform, the type of train and most often, the wagon list.
And you can carry your luggage if necessary, there is a bicycle section with straps to do so.
But, if you really want to spend a fortune, buy Glacier Slowpoke tickets in advance and perhaps bad weather might make this trip useless, ending up in a rolling restaurant with fog and clouds. Without the mountains of course. Your choice.