If you are planning to develop a native mobile application, that would cost you higher and consume time as well. Thus, cross-platform app development has gained popularity as it allows you to develop mobile applications that run on more than one platform.
Definitely, developing an application for different platforms can extend the development process, and by extending the process, you would be under the burden of the development budget. But, if you are building a single app for all the platforms with a single code base, you are saving your money and time as well.