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Based on the reference app suggested one can conclude that you want to develop an e-commerce app that allows third-party sellers registration on the platform. Now to create an e-commerce app that can fulfill this requirement would actually need not1 but4 apps/web portals.
1. User App
As the name clarifies it will be used by a user. Depending on the name shared by you in the question I assume you are well aware of what should a user app do in the case of an e-commerce app. For Example, Register, search, add to cart, checkout, and pay.
2. Third Party Seller App
Now, this might be a little complicated for some people as to what would a seller app do. The products listed on the websites/apps of Amazon/ eBay / Etsy are not by the platform themselves but by a third-party retailer.
Now, what should a third-party seller app offer to sellers?
3. Admin App / Web Portal
The backend activity of an e-commerce app like promotion, sellers and users management, Payment Management, content management, rating management, and many other activities are managed by the Admin in its portal.
4. Delivery App
The delivery app is used to notify the delivery agent of the product pickup location and product delivery location. The delivery agent regularly updates each activity on the app so that the user is kept informed about every activity of the delivery process.
Based on the above points the approximate estimate of the cost to develop an app like Amazon is $K - $K.