I've placed a converted sea container in our backyard (photo: https://www.msgtrail.com/about/) a few years ago. Insululation, floors, walls, windows, wiring, and transport (75 km by truck) cost approx EUR 12k. I had to install AC after the first summer because, although well-ventilated, it simply became too hot inside during warm days even though the studio is surrounded by trees. Using a sea container is a great start for this kind of object because it's sturdy and easy to adapt e.g. by cutting out sections for windows and doors. Cell phone reception is not stellar but adequate (2 to 3 out of 5 bars).