When I built my cabin in the woods 10 years ago I built a 1 bedroom cabin with bathroom, shower and kitchen and living room.
I built the 1 bedroom cabin to be able to full time live in once I retire and can get away from this Job that I have to be close too.
I go on vacation to the cabin in the woods a few times per year but hope to live there full time soon even if it means I find another job in the area where my cabin is.
For me I spent $15,000.00 total building the cabin because it has all the amenities of my regular home but if you just plan to build a simple cabin without bedrooms etc then you might build it for $1,000.00 to $3,000.00 for a simple cabin.
But if you want to fix the interior to be a full time cabin like your home such as drywall on the walls, bathroom, shower etc then the cost goes up.