Again, look into it, I'm not sure about Montana, but I know in many states it would not meet code requirements for insulation. Additionally, the roof/building would need to be designed to support the additional weight.
These types of things sound great, but when you try to make them meet code requirements they either don't or become very expensive to implement.
i am aware you are talking about an equivalent home. i'm still not buying it. these companies have spent the time and money to come up with these designs. they have the contacts for the materials and the labor. the people who work with them probably have some kind of contract to work for them for less than they would charge the public due to the scale they work at. no way is the random individual going to pull together all the required talent and resources needed to build the equivalent home for around the same price.
I am just saying to check into it. And I'm not talking about a "random individual", I am talking about contractors that build houses for a living, they have all the same resources as the pre-fab companies. They have contracts with material suppliers, they get contractor discounts, they know exactly who to hire for each particular job, etc.
Here is a recent example:
We had a couple come to us and asked us to prepare building plans for them. After months of laying out exactly what they wanted (the woman was very detail oriented, thinking about how she would walk through the house, etc.) for a house and completing the plans and they took them to two contractors for prices. The prices came back at approximately $225k and $245k. They thought both were too high, they ended up not using our plans (wasting $4k+) and buying a pre-fab because the price looked good, even though the layout and size were not the same. Then they needed to come back to us for a foundation design for the pre-fab. Then they needed to still hire the excavation contractor for the site work, the concrete guy for the foundation, etc. When they were all done it cost them $200k for a house that was not exactly what they wanted, smaller, laid out differently, etc. What they saved was they were able to move into the house about 2 months quicker. Yes, they saved $15k but if they had built the same house as the pre-fab the price probably would have been even lower. The house was about 250 +/- sf smaller, typically (around here) you can expect to pay about $150/sf so 250 sf X 150/sf = $37,500. So potentially the equivalent to the pre-fab house could have been built for $188k to $208k.
Now, Montana could be and most likely is completely different. Labor and material cost could impact things significantly. Just don't assume a pre-fab company with a nice looking website is going to better/cheaper than the guy with no website but does have his name on the side of his truck.
Another thing that I always think about when I see business names:
Best Builders Inc. vs Smith's Contracting <- I like it when the owner's name is right there, it tells me the guys stands behind his work.