With the general availability of the new Visual Studio Online Build and Deployment service, all Visual Studio Online accounts will receive four hours of free hosted build time per month. Build and Deployment is a task-based service that lets you author, queue, and monitor cross-platform builds on hosted or private build agents. This means that you can build for any language, on any platform, and you can manage multiple builds at once to get more throughput.
For more information, please visit the Build and Deployment Pricing Announcement
For more information about pricing, please visit the Visual Studio Online pricing