I was checking out the floor plans for one of these, and come to find out it quite inexpensive. The largest cost would be the way you furnish it, as in the interior finishing like flooring and walls. I can see this being pretty doable, even if it wasnt buried. Contract the construction and interior framing and finish it out yourself.
Here is a fellow in Texas selling one he built featured in an article:
A slide show of the home with price:
How deep they can be buried:
Here is the EMP benefit potential of them:
My question would be how radiologically safe are they if buried