Private Submerged living space have been offered at USD 52.000 per cubic meter. For example US submarines flagship Phoenix is 1500 tons of displacement and is offered for 78 Million USD.
It is clear that this is not a very tempting offer for housing beneath the waves.
On the other hand concretesubmarine.com offers a 200 ton displacement hull for only 93.000 USD - this would be 465 USD per cubic meter living space - comparable to US and european city housing costs.
The concretesubmarine.com hull is the space equivalent of a 60 squaremeter apartment...