Так вышло:
SELECT
m_users.*
FROM m_users
LEFT JOIN mc_rating ON m_users.id = mc_rating.user_id
LEFT JOIN mc_offers ON m_users.id = mc_offers.driver_id
GROUP BY mc_rating.user_id, m_users.id, mc_offers.price
ORDER BY ( SUM(mc_rating.name) / COUNT(mc_rating.name)) DESC, mc_offers.price;