Return the cost of a given namespace, including fees.
        Returns {'amount': ..., 'units': ...}

def rpc_get_namespace_cost( self, namespace_id, **con_info ):
        """
        Return the cost of a given namespace, including fees.
        Returns {'amount': ..., 'units': ...}
        """
        if not check_namespace(namespace_id):
            return {'error': 'Invalid namespace', 'http_status': 400}

        db = get_db_state(self.working_dir)
        res = get_namespace_cost( db, namespace_id )
        db.close()

        units = res['units']
        amount = res['amount']
        ns = res['namespace']

        if amount is None:
            # invalid 
            return {'error': 'Invalid namespace', 'http_status': 404}

        ret = {
            'units': units,
            'amount': amount,
        }

        if ns is not None:
            ret['warning'] = 'Namespace already exists'

        return self.success_response( ret )