Its not only about buying "mini hydroelectric powerplant" ... There are a lot of things that you need to take in consideration. I was thinking of this as well, and have done research how to do it in my country(even if its 3rd world its expensive). In total it would be 3.5m euros.
In the background of everything, you need to:
1) Buy land
2) Take shit ton of permits from government
3) You need to find PERFECT land, where you are not harming nature, or people(again government)
4) After that you need to find contractors
5) And in the end you need to start working with electricity and hydro pump
Timetable for doing all of this, because you can't do 1 if you don't have another(permits) can take up to 2-3 years. So when you look time needed to do everything, its to much work honestly
What if you buy an already existing hydroelectric powerplant. ROI on the electricity production alone is like 20 years so there would be many intrested in selling.
You just connect to the miners and that's it. No permits needed? Or is it still better to just pay for the electricity?