That's a good idea about the metal detector @noroof. I wish i knew how to get one on loan!
Avo, our back garden is really REALLY bad near the building. Basically a lot of mud as it has been a wet summer here. Lots of building material spread about. We have a v wide plot and an access road at our back gate. They made full use of that! Spread out. Had a little triangle of untouched grass but they have spread a large tarp now and collecting rubbish for next skip on it. Keep telling myself it was mainly moss anyway but can't help but wish it gone!
I also moved some plants out of the way and when I saw things too close to anything I really loved (like peonies) I moved them!
Ours is only single storey so I can't help with price - sure others will know.