http://compsci.ca/blog/profitability-in-video-game-industry/
Sony, that also develops their own games, is scaling up its internal development resources. Sony is now employing over 2000 developers across 14 game studios. This makes for a 140 staff game studio, burning through $20 million to publish a game title for a single platform, once every 2 years. Sounds huge, but if you do the math, an average employee in such studio still earns less than a programmer in other high tech industries.
So, if you back out the math, this comes out to $715K per 10 developers per year, which sounds really low when you count salaries, 30% overhead for taxes, benefits, etc + infrastrucure (building, servers, etc). So let’s call it an even $1 million per 10 developers.
I imagine that some companies do like SD did in their very early days and take on side projects while the do the primary game development (map expansion backs for the GOTY version, some commercial work)
To cover the remainder though, I imagine that a publisher would have to cover some of their expenses with an advance or retainer.