Well lets see:
PSP games have small budgets which means they don't take that many developers' (years).
The game would have likely been in pre-production before KZ2 E3 trailer was released with work starting in earnest when development kits were released so make that some time in 2005.
Guerilla Games has a lot of staff between on site testers and coders/developers considering they had to create a lot of high value assets and if you believe their PR they created GB's and GB's of unique content for each level if you consider their claim of over 2gb? a level.
They used outside contracters for some of the work like for example the AI was outsourced and they would have had to have used a lot of motion capture for the animations.
All in all, one expensive development effort, once they take marketing and publishing costs into account I wonder how much change they will get out of $100,000,000 U.S for the game?
Tease.
