Here's a pointer to salaries from 465 developers who tell us they use React.js, by city (but you can break it down in lots of other ways): http://www.payscale.com/research/US/Skill=React.js/Salary#by...

Disclaimer: I work at PayScale

Those three locations will increase the cost by a fair amount. Id try hiring a remote developer located in the US. Less expensive because they tend to live i areas withower costs of living.

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.

I would suggest something similar. Looking for remote developers if possible those are 3 of the highest salaries markets.

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.

Id say there is a higb likelyhood they will need someone witg react and native expeirence.

Come out to the Boston react native Meetup and talk to folks; it's a great community!