There’s a threshold for being cost effective. And being cost effective would also mean to minimise needs accordingly. Being satisfied with minimal interventions for being comfortable in a shelter for a context.
Pre planning for cost effective needs to be subsidised by an organisation. Who pays for pre planning? Costs are always borne by someone to conceptualise ideas for mechanisms of implementation. If the world is dependent on each other- each is paying for the other. Ideas and efforts need to be paid for always whereas material costs could minimal and likewise physical output. Building something oneself is also a cost incurred by oneself on oneself. Cost effective applies to situations where material efficiency is taken into account. Also appropriate quotations for costs depend on the scale of projects too. There could be individual houses