It's the investment cost of the miners measured in Bitcoin which is the problem. There is just nothing left to cover the risks you are taking, even it looks like you could mine back the Bitcoin invested in an acceptable time frame. It looks completely different if you already have the hardware.

Regarding subsidies for hydro power it depends if you get any - there is only some money if you newly renovate your power plant and can prove that it will increase the yield by at least 20%.
If that's the case you can choose between getting some money for each kWh for the next 13 years or a fraction of the investment.

It's a pretty sad story - many power plants in Austria stand still because the ROI times for investing are >50 years. Also there are many ecological rules and other regulations, until ~2024 all power plant owners will be forced to install a fish ladder which often consumes the profits of ten or more years.