"Destiny," which comes out in the fall, is as of right now the most expensive video game ever made: $500 million.
The $500 million price tag breaks down to $140 million for development costs, according to a leaked contract between Bungie (the developer) and Activision (the publisher), and the rest being marketing, distribution, royalties, etc.
Just note that the most expensive film ever made, "Pirates of the Caribbean: At World's End," cost $300 million.