I hope I may hop on this thread, even if it is dormant for a couple of days now. But the question is still a good one and the answers might be different as time goes by.
I have a Siglent SDS2000X+ for about a year now. The problem of such a capable tool is, that it does much more than a casual hobbyist needs regularly. At least much more than I do. I do find my way around with the most common tasks and I have the manual ready to help me with more sophisticated ones. But it's one thing to "know" about a feature you could use in certain situations and to be ready to use it when you never have seen such a case in reality. So I'm thinking about adding some kind of "problem creator" to my toolset to gain (and keep) better knowledge to track them down - and get more confidence in using sophisticated triggering.
With this scope, aiming on the "STB3 demo board" seems straight forward. On the other hand, the new Batronix seems quite useful too and has a way better documentation. The STB3 manual is more a collection of screenshots. Pico makes quite some PR on their MSO test board - which looks exactly as the Batronix board.

Are these still the actual options? These parts seem to be quite expensive considered that they look just like "some small microprocessor and a couple of connectors".

An ESP32 seems to be of comparable complexity and goes for about 3 bucks.

It looks a bit like calculating the "merchandise" to match with the premium products, like a Lexus keychain is more expensive than a Dacia one.
Certainly I do underestimate the challenges creating such device and if they are meant for teaching classes, then you invest just once and use multiple times. But is such a device a one-shot, gathering dust, once you walked through the exercises, or is this tool a long lasting benefit that you grab regularly?
For 200+ € one could buy an entire scope that is not even a toy or a pretty capable signal generator...
Are there any alternatives that better fit for a hobbyist budget? There does not seem to be a market for "pre loved" parts either. Which may be a good thing, as it suggests, that people tend to keep them instead of trying to sell them once they have the lessons learned.