Ideas for a cheaper, apealing home.

Exterior:
Rusted Metal Sheets : 2x8ft Rolled Steel : $5 sqft
--- This material makes a nice, rusted red appearance after six months.
Cement Board : Stain peach, then add a wood stain. $1.50 sqft
--- Gives the appearance of wood board siding.

Exterior Walls:
Exterior Walls are currently planned be 6" thick wood walls. Despite Tennessee only requiring 4" thick walls, the additional thickness will aid in insulation.

An alternate idea is to build a Straw Bale house that is a 4x4 stud frames with straw bales in between. This would certainly provide good insulation, and I'm sure hay bales are quite cheap. Here's a page with a few house plans (The "coil" looks interesting.) I wonder if there would be a problem using ferrocement instead of plaster? (Ferrocement is more of a concrete then plaster.) There seems to be a good site for it too.

And then there's the potential of a solid concrete home. I would have to do some math to see if that would be an affordable option though.

Interior Walls:
I cannot think of a cheaper inside wall with the same thickness then standard 4" wood and drywall. Any ideas?