Ratchet & Clank: Size Matters isn't the only PSP game being slashed down to the budget price of $20. The top-down shooter, Killzone Liberation is also joining the bestselling Greatest Hits lineup.

This is a terrific deal for a solid action game. Certainly, Sony's trying to raise a bit of awareness before that little PS3 game comes out. You know, that game called Killzone 2. For those that pick up Liberation, don't forget to pick up the free bit of DLC for the game: it includes Infrastructure multiplayer and an additional single player chapter.

This article was originally published on Joystiq.

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