Here's an idea for building a cheap house: Use what others are throwing away. This woman is using closed cell foam. It has to be disposed of, because of an envirmonmental law passed in the Ozarks. She is using them as load bearing supports. It looks good, but one doesn't ususally think of foam as being that strong.

Carrying this idea along, what they mostly try to give away on Craigslist is concrete chunks, mattresses and old appliances. I could see using concrete chunks like rocks in a slipform concrete wall. Maybe you could build a post and beam house filling in the sides with mattresses. Appliances, well maybe you could have a wall of microwaves. A refrigerator, washer/dryer/dishwasher wall would be quite wide, but at least they would all be more or less the same thickness. You could even have the doors open to the inside and have built in storage. It goes without saying that you would have to build this somewhere where there are no inspectors. I hear rural Vermont is like that.