Lets just go with $50 and $20. If you're looking at that on top of the cost of a raspberry pi, comparing that to a super low-end Android phone, used, for something like $80-$100, is that really the way to go? The OS is different but termux has enough features, especially after rooting, that you can probably run whatever you're shooting for. Of course as a hobby, the parts that you find fun don't have to be the parts that I, or anyone else finds fun, so don't take this as me pissing in your cereal, it's more like there's the milk part and the cornflake part and so different strokes for different folks.