Also my suggestion this company https://mlsdev.com/services/custom-software-development
It depends on huge amounts of various factors. I mean, you can create an app which just says "Hello, world!" and it won't cost much. So, first of all, you need to think out what you need. It's the first step that will determine almost everything else. Probably launching an app and maintaining it won't be that cheap (it's so for many projects) and there are ways to make it cheaper, of course.
In this thread, there are many decent tips and recommendations but I want to elaborate on outsourcing. Even though it's a bit more complicating (working with several companies rather than with one only) it's cheaper in most cases. I always prefer this model. For instance, I decided to work with Awesomic design services instead of having my own designers because it's simply cheaper and their UI design for my apps meet my needs. The same approach should be in other fields.
Mobile apps is a tool among your assets and you need it to deliver on what your goal was in the first instance.
that being said,i would recommend my services ,
I am a Software engineer and a Web Developer for over 10 years and getting your app to do what you have in mind would require i get some additional information from you.
my portfolio is at www.afeezbadmos.com