Cross-Platform Goods Marketplace App

I’m building a mobile marketplace where buyers and sellers can register, list physical products. The core flow is straightforward—browse, chat and they deal themselves —with the ability for sellers to manage listings, prices, images, and stock from their phones... (Budget: $750 - $1500 SGD, Jobs: Android, Android App Development, App Design, App Store Optimization, Backend Development, iOS Development, iPhone, Mobile App Development, PHP, User Interface / IA)