How much does it really cost to build an affordable house (for real)

How much does it really cost to build an affordable house (we're talking

something under 50 square meters) using alternative construction

techniques, such as containers or prefabricated structures.

Aside from having to lay a foundation (or if you put it

on pillars, it will have cost less), what is the final cost for the

house alone?

What are the most economical, yet truly

durable methods for doing so?