Find out what recycled materials are around. Or what is produced locally.
Shipping is $$$. And/or waste products. 2x4's 18" to three feet long, with
enough, will build a house w/ solid double walls, insulation between.
Tires. Beer cans filled w/ water, imbedded in cement. A bottler MAY fill
them for you. Cheap. Reuse & recycle.
If you truly wish to save money, learn about alternative construction. Be
ready to work. It'll take twice the time you think it will.