There are two main options, when it comes to making money from an app :

1- sell a small (cheap) app to many people

2- sell a big (expensive) app to a few people

While it is true that the most successful apps are usually pretty complex and expensive to produce, there are ways to make money with small apps. Games are a good example, as some hugely successful games are human-sized projects.

One thing : Starting a project with money as your unique goal won't lead you very far...passion is a way bigger motivation (that often leads to success, too).