Tickets for Bernina Express

You can buy the Bernina Express tickets on their own website, if you want the named Bernina Express train.
https://www.rhb.ch/en/panoramic-trains/bernina-express

Or you can ride the regular regional trains which have frequent departures. Book those on SBB.ch and look for a “special Offer Price as it is considered an international journey. We paid 32 CHF for two tickets, booking 22-3 months in advance.

From Tirano to Heidelberg: are you aware this is a journey of 10-11 hours? You can actually buy that ticket on bahn.de and I am seeing one-way prices as low as 39,90 euros for purchase 2 months in advance.

What do you mean about a “round trip ticket to and from Germany” being cheaper iven if you do not use all of the ticket? Are you talking about flight tickets or train tickets? You must be very careful with throwing away part of a round-trip flight ticket, so I hope that is not what you are talking about.

On the throw away ticket it would be a train ticket. It can be cheaper to buy a round trip train ticket, Heidelberg to Tirano, including the Bernina express. We just wouldn’t use the “to” portion Heidelberg to Zurich. But would use all the rest of it. Yes, we are fine with the 10-11 hour ride from Tirano to Heidelberg.

You're right to look for DB round trip tickets through Switzerland which are often much cheaper than buying a ticket to or from Switzerland.

I do see the problem with getting your tickets on the DB website. Not sure why that doesn't work. Perhaps give them a call.

Once you have your base ticket, if you want the real Bernina Express, you can get just the supplement on the Bernina Express website. Look for the itineraries marked "Bernina Express" (the others are plain regional trains that run on the same track but don't have the panoramic windows or nice service). When you get to the "Passengers" part of the online process, select "Ticket Available" to indicate that you already have a ticket, you just want the Bernina Express supplement.

Looking again at the bahn.de website, I see tickets from Heidelberg to Tirano in early April for around 119,80. You must force it to route you on the Bernina Express route by putting in Pontresina as an intermediate stop, for a few minutes. This route also has a change in Chur so you should be able to board there, forfeiting the earlier portion of the trip. However, as the Bernina Express departs Chur at 8:32 am there may not be a connecting route from Heidelberg that you could buy. If there is a later Bernina Express train I did not see it, but I did not have the time or the patience to look through the whole schedule.

I see the price of a ticket from Chur to Tirano on the Bernina Express panoramic train for 3 April, purchased on SBB.ch, is 64 CHF. You would have to add the reservation cost.

I still see no advantage in buying this as a round trip ticket from Germany.

I remember now what we did: not a round trip, but we did buy a one way on DB from Freiburg im Breisgau to Tirano, even though we were only actually going from Chur to Tirano. It was significantly cheaper than buying Chur-Tirano from SBB. Then we went to the Bernina Express website and purchased the reservation supplement.

I just checked DB and they can sell a Freiburg-Tirano ticket, but not a Heidelberg-Tirano ticket. Not sure why.

As I noted above, bahn.de does sell a ticket from Heidelberg to Tirano. But it is not straightforward, and not all routes follow the Bernina Pass route. You must force it to show that. And of those, I did not see one in April that included the actual named Bernina Express train, because of the timing. The cheapest fare for early April I saw was €119, but it may be less on other dates.

It just does not seem worth all the fiddling around to get the round trip ticket that “someone” recommended, as there does not appear to be a price advantage at this late date. They can just buy from Chur to Tirano from the Swiss site. And then Tirano to Heidelberg on barn.de.

Seat61 explains a way to snag very low fares from Germany that take you along the Bernina Express route. I haven't re-read that information recently, but it made sense back in 2016 when I first came across it.

Like acraven suggests, the man in seat 61 knows his stuff.

I followed his directions on a 2016 trip and rode from Basel to Tirano, including a seat in the panorama car on the Bernina express for 29.90 Euro, plus a 5 Euro supplement. Fully legit and easy-peasy.

The juicy details (from avraven's link):

Bernina Express from €29.90: How to book cheap tickets & kids under 15 go free!

Swiss fares are expensive. A 2nd class ticket from Zurich to Tirano costs CHF 90 or €85, even before you add the CHF 10 or CHF 14 Bernina Express reservation fee. The Swiss don't offer any cheap advance-purchase fares on this route, only the expensive regular flexible fare.
But there's a clever & perfectly legitimate way to pay as little as €29.90, and if you've got kids under 15 they go free too.
German Railways (Deutsche Bahn) offer cheap advance-purchase tickets between any station in Germany and any station in Switzerland from €29.90 in 2nd class or from €59.90 in 1st class.
Singen (Hohentwiel) is the last major stop before the Swiss border. You can buy a ticket from Singen to Tirano from €29.90 and simply not use the Singen to Zurich part. Or vice versa northbound. This perfectly legal, and nobody knows or cares whether you use all or part of the ticket, this is not an airline!
Naturally, these fares must be booked in advance, the fare varies like air fares and the cheapest fares can sell out. You can only travel on the specific trains you book, no changes to travel plans and limited or no refunds. But booking this way saves up to 65% off the regular Zurich-Tirano fare. Accompanied children under 15 go free if entered as children in the normal way when you make the booking.
Booking used to open 92 days ahead, but DB have now extended this to up to 6 months.

That is good information, and confirms what I saw on barn.de. The problem for the OP is that the lowest fares from Germany to Tirano on the Bernina route appear to be gone for early April dates. May was as low as 44 euro when I checked, but early April much higher.

Thanks so much for all of the help. We did get RT tickets from Heidelberg to Tirano. Then just simply bought seat tickets for the Bernina Express. You have to scroll thru a lot of optione and follow “Man in seat 61” to the letter. We have used his website for many train situations and he has never let us down with the information he provides. Anyway, thanks to everyone!