I wonder how much it would cost to purchase an island with 10-20 people and build houses on it. Could you live there in a sustainable way? Possibly seems like an interesting way to live.
You can buy a small (~2 ha) undeveloped island for as low as 100,000 USD. Bigger ones cost more depending where they are located. However I saw really big islands (~2,200 ha) for about 2M USD in Chile (I think that is cheap considering that a luxury apartment in my city, Florianópolis, can cost way more than that). Current solar energy solutions and biogas production from waste can form a solid base for a sustainable community.
2,200 hectares? Do you have a link for that? That can't be right / seems amazingly cheap (also if compared to that small island, too good to be true). If you split $2m between 20 people you get 110ha for $100k. 110ha is massive.
I have a property developer friend who had the idea to create a sort of luxury village in Southern France where successful people from the arts / entrepreneurs etc could meet. People that had achieved financial independence and weren't "part of the system". Sort of like a safe enclave to exchange ideas. He did well + things were progressing, but during the financial crisis in 2007 banks pulled out (€50m in loans) of the deal and wiped him out.
I honestly wonder how many people would be interested in living like this.