I work at a e-Commerce solutions firm that provides SaaS packages with a one-time $500 set-up fee and annual flat rates starting at $350(although in your case the need for payment integration would bump this up to 500/yr), which provides you with an e-Commerce website, along with a web portal and mobile application to manage your e-Commerce website. If this interests you, feel free to reply to this bid, check us out at goopter.com.