For the structure of the house, we started shopping storage buildings. Found most 16x40's are selling for $16k. I found a local builder who will build a portable building on your property in one day. He's said he'll swap to 2x6 on 24" center walls for me and mylar OSB for the roof underlayment for $14.9. I was pricing out the materials and I think I can do the same for about half that price but it'll take us two weekends. In the scheme of things and since I gotta finish the inside anyway, that time is not that critical.
What I've found is instead of T1-11 or hardy board, you can use a product called LP smart siding. It's about $45 a sheet and for and extra $10 a sheet it will come with mylar radiant barrier on it. So this means raidiant barrier on the roof and walls! I expect that 2x6 walls will give us R21. The dutch barn roof will make her ceiling height 10'8" inside so it should feel roomy. I'm going to put awning windows popping out of the roof tin to let a lot of natual light in. She'll have a laundry / mud / inverter room at one end with an overhead storage rack. The kitchen/living room /bed room will have full height ceilings and storage shelf over the bath room for boxes.
Fire away with suggestions.....