My folks did this in 88~90 (I was 8~10). It was 800 square feet with a tiny 1.5 bath. Instead of garage doors, they framed the openings and sided them. It was basically the foot print of a 3 car garage but the third bay was the bathroom, kitchen and laundry. They had their king size bed on one side, I had a twin on the other. Our clothes hung on 1/2" pipe racks between the "bedrooms".
It was quite "cozy". My grandparents lived a few miles away so I spent the night on weekends there most times.
During the 2 years we lived there they built the house as they could afford it. Foundation, wait; dried in frame, wait; electric & plumbing, wait; etc. When they were done, it was paid off. They saved quite a bit doing what they could on their own and GC'ing the rest. It is a nice house, 2400 sqft brick ranch, but it is basic. But at the time it was better than the house in the 'burbs we moved out of and served our needs.
If I remember right, it worked out to $21 sq/ft to build. Probably more like $80~90 today.
