Hey, I am a frontend developer and from the last 6 months, I have been developing screens for react-native applications like ecommerce apps and etc. I am highly experienced in converting XD, PSD, Figma designs into React Native Screens. So, if you want someone to develop your screens part. I can be that guy, and will be charging low too, which will leave you with a good budget for you to hire someone who can alongside handle the api integration and stuff. I can easily develop your application and even really fast. I can see that your mockup only contains 4 screens and if there are only these 4 screens, then i will be completing this in just few hours and will take 25USD only. With increase in screens, price and time will increase, but not that much.