Inspired again

I’ve just been doing some more research into earth-sheltered houses and come across this:

Which is a site about the Cumbria underground house, also seen on Grand Designs.
I really like this house, especially this image of it, which fits our ideas about having communal space at the front, very well:

But I’m less pleased to see that it wasn’t cheap.  I wonder why it cost so much money?

Update

There’s not much happening for us at the moment on the off-grid front. We’re focusing our money and energy on trying to get the house ready to be sold and we’re painfully aware that the housing market is in steep decline, so it might not sell and we have to be ready with Plan B: [...]