Although there are many subgroups of app developers and you can pick one based on your needs. Enterprise-level firms are the most expensive option but provide the most robust and rapid means to develop your software.
These companies can handle every step of the app development process for you, from concept to testing and release. They call for the highest investments, and their designers and developers are typically in-house staff.
Then, you can find smaller studios. Some of these studios have as few as two employees. They accept fewer projects, but complete them to a high standard, and often have specific domain expertise in one or a few app categories.
Finally, there are freelancers. It is possible to find someone prepared to take on every aspect of the project, including testing, coding, design, and publishing.
But those who can do it expertly are extremely rare and command high rates. It is possible to hire freelancers to help with app development, but doing so may bring more stress. So choose wisely.