A much cheaper alternative is a bigger electric jackhammer with a spade bit on it.So now the digging. I'm am not looking forward to doing this trench by hand. I've calculated it at 20×.3×.75 = 4.5m³. That's just to get the duct and power to the garage. Probably double that to do the trench the full plot width to allow for future drains etc.
I REALLY need a digger. Keep mulling these Chinese ones...
I have had to trench across the yard for new cables out to the solars etc, and rather than get my jcb and rip a big trench across it with all the resultant destruction that ensues, I just put the spade bit on a 3kw electric demolition (jack) hammer (the type that take hex with a flat bits, and cant be used as a drill and weigh 40+ kg) and cut out a small clay spade bits widths channel to depth and laid it in a flexi duct as per regs.
The demolition hammer is also usefull to drive metal fence posts in with a post bit. I was expecting it to be pants for this but its surprisingly good at it.