Besides using straw bales and cob, light clay, adobe, wattle and daub or sandbags etc
also then look at using rubble trench foundations rather than conventional concrete foundations, stone or urbanite for foundation base walls, your own harvested poles for structure (non-toxically treated or biodynamic harvesting methods).. second hand windows and doors, second hand fittings (most 2nd hand goods require lots of running around and TLC so requires time), light clay roofing insulation, earthen plasters, home made paints etc.
Using recycled bottles to build walls or windows can also be a way  to create beautiful patterns of light. The walls create good insulation.

(Also please see  " Are there any other natural building technologies other than Straw Bales? ")