We can guesstimate based on what has leaked out. Dev time has varied between 3 and 5 years depending on who you believe, so average it to 4 years. Team size has varied between ~50 near acquisition by Sony, to ~200 at peak. We can average that out as well just for the sake of argument. So a guesstimate at say $50,000 average yearly salary might be:
Year 1, 50 people = 2.5 mil
Year 2, 100 people = 5.0 mil
Year 3, 150 people = 7.5 mil
Year 4, 200 people = 10 mil
So a naive guesstimate might be 25mil spent on salaries. However, were there any outsourcing costs, like art perhaps? Any overtime costs? Any external team costs, like perhaps parts of Sony q/a or Sony tech teams? Any perk costs like team trips, in office masseuse, free food and sodas, etc? Yearly rent and utility costs? Marketing and advertising costs? The euro probably factors in as well since I suspect a $50,000 US yearly salary guess is likely low. After the game is done there are still shipping costs, blu-ray disc replication costs, as well as payments for better placement in stores, etc. It all adds up real fast.
As you stated, it's weird that people often forget about the many other costs associated with running a business vs just salaried employees. Even with salaries, the actual cost of an employee is much higher. In California, you can get upto a 35% employee burden (employee tax, benefits, insurance, etc..) Thus a person making 100k a year is actually costing the company 135k.
Then, as you stated, there are still have costs for:
Facilities: rent, utilities
IT budget: Computers, servers, backup system, IT staff, Internet, software licensing
Legal: compliance, IP licensing
Administrative staff: HR, Accounting, admin assistants
Office supplies: paper, copiers, scanners, pens, etc..
All these costs go up as you ramp up the staff but often seem to be neglected. Perhaps, it's due to the lack of exposure on these aspects of a company to most employees that makes them neglect such factors but start getting to a place in a company where you're looking at P&L's and you'll soon become painfully aware of these burdens on a business. It's not just "headcount."
As for sharing tech and it's "value" it's an endless argument with those who look for justification. At some point you have to close the book on a project. Once the project is complete, the budget is assessed. Any gains for future products will be reflected by the lower costs on those projects. It'd be an impossible accounting job to sit there and go "oh, because of Killzone 2, we saved 10% on MAG, 3% on HS2, 7% on Uncharted 2, so looking back Killzone 2's actual cost was X" This is a feel good mentality in conversation but is laughable to apply towards accounting principals. Many projects, even non technical, can reap rewards for a company down the road but they still had a production budget that closed once the product was shipped/implemented.