Best Buy offers Ratchet & Clank for PlayStation 4 for $19.99. Opt for in-store pickup to avoid the $6.99 shipping fee. That's $8 under our July mention, the best now by $10, and the best price we've seen.
Of note, My Best Buy Gamers Club Unlocked members can get it for $15.99 via in-store pickup. (A 2-year Membership costs $30.)