As of 2010, the average development cost for a game (excluding marketing budget) was between $18 million and $28 million USD. It's going to be a lot more now since developers have to put a lot more time into developing the game, especially textures.
As for the revenue "always in the 100s of millions of billions", no.
It's only the AAA titles get hundreds of millions or billions of revenue per game. The same AAA games (excluding marketing costs) usually cost between $50-$100 million. You then have to add on the $50-100 million marketing costs and they would need to get $100-200 million just to break even on development and marketing. You will still have to include the other costs such as hosting servers for multiplayer as well as developing patches.