Normally when I think of Google I think Java and Python. Other services including Heroku and Azure support a wide range of platforms, including Node, so it's exciting to see Google offering MEAN.
The developer guide is here: MEAN development stack on Google Compute Engine, but it's worth noting that the MEAN stack can be brought up with click-to-deploy. That means you can get MongoDB, Express, and Angular running in minutes, using a web-based wizard.
I'm not exactly sure how the pricing works with MongoDB, because SQL database pricing is different from Compute Engine. I created a click-to-deploy MEAN project and it seemed to show all the resources under Compute Engine, so I think that means all prices are based on CPU/disk usage.
I make a lot of Express apps, and Google's developer tools (including the web console) seem compelling even next to Heroku and Azure, so I'd definitely like to try this for a real project soon!