Costs for our construction project

Wow, those are completely different figures. That definitely exceeds our budget...

In my opinion, there would be space for a moat. Is that the best installation method?

Hello. Whether the ring trench is good or bad depends. But you can build it yourself. See slinky method. Just google it. There is a forum where it is explained in detail and help with the calculation is also offered. P.s. it is definitely the cheapest if self-built.