On average in what city?
Do you want to oay average?
How will you test their skills?
I guess the best test of their skills would be a referenceable experience. A github portfolio or something.
BTW, react native is something rather new. You wont find anyone outside of the core group of react native developers who really knows it. You will probably have to include some time for training.
In terms of skill set. If you hire React developers they should do fairly well in terms of development.
Unless of course your app will need a lot of customizing then you may need someone who can understand and develop in objective-c/swift and/or Java.
Disclaimer: I work at PayScale