Today, by chance, I found this show about underground housing on HGTV.
Subterraneans

The thing I found most interesting, was that they covered almost as wide a financial range, as is possible. There was an underground mansion topped with a mirrored glass
pyramid, and A compact little cabin in Idaho, which was built for 500$.
There were several examples, some of which I would absolutely love.
I have been trying to find the video online but have been unsuccessful so far.
There are some pics of each example online.

(EDIT) Earth sheltered design would be more accurate for most of these examples.