Supposed to be DIRT CHEAP from what Im reading.Maybe for the bales but it would end there.
Anytime you do anything in construction that is unconventional it will cost you more if not for labor but maybe both labor and materials.
The things to consider before building a bale house are too many to mention.
How are the window and door jambs attached to the bales...you know so they don't fall out in a wind storm or a slammed door?
Are the walls (bales) connected to the foundation with mechanical fasteners?
Are the bales fire resistant?
The straw will compress and shrink over time. What will that do to the solid plastered surface?
How do you run plumbing and electrical in the wall and how do you secure elecrical panels, switch and light boxes to hay bales?...not to mention pictures amd window coverings.
It seems to me that the exterior of the house ( the wall's building materials) would be a rather minimal cost. The real cost comes from all the stuff that goes underneath, on top, and ( especially) **inside**.
Treating the bales with boric acid should help with insects and give some level of fire retardation too.