I have a Wurzelmobile I made over the last year, not up to your specs, but it keeps the rain off, has solar power and a cosy stove, so good for off grid, I also fitted a good stereo system, fridge and loo with shower, sink and hob.
The wood came from partly from a tree I had to remove in my work, home milled and moulded.
Cost in total is well under eight grand with a 2010 van base.