Torwag & Kamikaze :
I'm sorry if my remark came across as too harsh, it was not the point.
I'm fully aware that the additional costs are due in part to the power needed by a python interpreter (compared to compiled C code), in part to sustaining the project (which is good), and in part to small batch runs for addon boards (which is unavoidable).
It still remains that compared to the dominant Arduino ecosystem (which has the exact opposite advantages), the joy of coding in python instead of C comes at quite a price.
Also, the "coding in python" part is somewhat relative: it's python syntax, yes, but the way you need to use it to get around the microcontroller quirks makes it a very different experience. Even for an experienced desktop programmer, the learning curve is not negligible.
Last year I did the exact same project twice :
Once with an Arduino, as a total newbie to the platform, by reusing relevant C code I'd found on the Web.
Adapting it to my needs was painful (I hadn't touched C for many years), but all in all it was a day's work.
Then I redid it on a Pyboard, and was surprised at how hard it felt. If it hadn't been for this forum I would probably have failed.
One area where the Pyboard shines, though, is the USB mass storage mode: being able to change code and/or data anywhere, any time with a simple text editor (even Notepad

) is really invaluable.
(and yes, I would buy a faster pyboard2 instead of yet another pi Zero

)