According to this US PS Blog post, Ratchet & Clank Future: Quest For Booty will release on PSN on August 21 in the US for $14.99.
The game will also be available in Europe on the same day, releasing in Japan on August 22.
The game is a “pirate-themed sequel to Ratchet & Clank Future: Tools of Destruction. Even though Q4B is a downloadable game, it packs all of the AAA-production punch you’ve come to expect from every Insomniac Games title.”
More detail through the link.