Update: I have to say that the blog I link to here is either a very well connected anonymous insider blog or total BS. Reader beware. Still, it sounds plausible.

Here is some industry scuttlebutt about Killzone 2:

[...] that figure was actually €21 million ($30 million) and it has only gone up from there (by gone up i mean it has doubled to €42 million/$60 million). by the time killzone 2 comes out it will dethrone shenmue as the most expensive video game ever made. the game should have cost the former figure but guerrilla's managerial lacks any sort of financial or work allocation skills, the studio has high turnover and a few other things. because of this incapacity a nice portion of the team at studio cambridge is assisting in development. to top this off the game may be pretty but it's barely mediocre and past the point of no return. the september release date floating around will without doubt be missed if guerrilla sticks to their intention of not releasing the game until its done which will be early next year.

There is more, but not much more.

Killzone 2 is big, bigger than Guerrilla has ever made, and it is super-important to Sony, so the pressure will be enormous. It won't be the first nor the last title that is finished by bloating a team beyond decency. And that has to be expensive when your offices are in the center of Amsterdam.

I know some people working on Killzone 2. I think it will look great - really great. But I have no clue if it will play better than Killzone 1.