Get the price for a namespace
        Reply the price for the namespace as {'units': "...", 'amount': "..."}
        Reply 502 if we can't reach the namespace for whatever reason

def GET_prices_namespace( self, path_info, namespace_id ):
        """
        Get the price for a namespace
        Reply the price for the namespace as {'units': "...", 'amount': "..."}
        Reply 502 if we can't reach the namespace for whatever reason
        """
        if not check_namespace(namespace_id):
            return self._reply_json({'error': 'Invalid namespace'}, status_code=400)

        blockstackd_url = get_blockstackd_url()
        price_info = blockstackd_client.get_namespace_cost(namespace_id, hostport=blockstackd_url)
        if json_is_error(price_info):
            # error
            status_code = price_info.get('http_status', 502)
            return self._reply_json({'error': price_info['error']}, status_code=status_code)

        ret = {
            'amount': str(price_info['amount']),        # helps JS clients that can't parse big ints
            'units': price_info['units'],
        }

        if ret['units'] == 'BTC':
            # v1 compat
            ret['satoshis'] = price_info['amount']

        return self._reply_json(ret)