Yes, a trailer would be much cheaper.

Looking at the picture, I feel it must have cost a lot, maybe 50k, to construct a tiny amount of space. Their neighbors looks like a much nicer cottage.

https://cms.zerohedge.com/s3/files/inline-images/2022-07-25_14-11-31.png?itok=y5Tzxm71

I think they are either bad with money or were forced by circumstance to pick such a bad option.