I buried our power cable 60 cm deep. I laid the cable on sand and removed all stones. I covered the cable with cable cover caps. That is safe and works well.
No, a mini excavator is not needed here. No kilometers are being laid. I buried our cable under 80 cm. With a decent mattock and shovel, that worked excellently.
I also believe that a mini excavator is not necessary to dig the trench. That can be done with a shovel. We laid it 60 cm deep, so the frost cannot harm the cable.