You can scale a SaaS application on Railway by creating isolated environments, such as Staging, for testing new features without affecting the production environment. This is achieved through continuous deployment and automated testing of code changes in a live environment. Railway automatically deploys the latest commits to the main branch of the connected GitHub repository and supports both vertical and horizontal scaling approaches. To reduce costs, you can use app sleeping, reduce egress fees by using private networking and distributed storage services like MinIO, which do not incur egress fees. Additionally, implementing HTTP caching and utilizing global CDN networks can improve performance and user experience. By following these techniques, you can optimize your SaaS application's cost and scalability while maintaining a high-quality user experience.