I heard one of the significant costs was the foundation and needed accommodations to meet California building codes for such a unique building. To pay for it I believe the dues are 3K a month, in addition to the community HOA which I believe probably subsidized some of this cost as well. Also as Steve pointed out the 4 penthouses, which are really stunning, but wow you have no yard or anything, just the apartment and patio basically. I don't know if they took a loan out, which I suspect they maybe had to, in addition perhaps an assessment to the members?
They also have this community car warehouse call The Vault which is quite over the top as well, like everything at Bighorn.