I run a NUC11 so about 10W. 15-20€ per annum assuming a single tariff at 0.17€ per kwh.
It can use up to 30W but only during heavy load which may be like 8 hours a week. But electricity is also cheaper during off peak hours so it averages to about that (we have 5 tariffs).
Load is NAS, media server, homeassistant and a usb zigbee router, *arr stack.
Power usage was my main concern and wanted something eco friendly.