Two stores with the same design can differ in price several times over. Looks are secondary here: most of the time goes into catalog logic, checkout and data exchange with other systems. The guide prices on this page start at $2500 for a basic version, but the final figure depends on the specifics of your project.
Not everything has to launch at once. A sensible first version includes the catalog, a clear product page, a cart, one or two popular payment options and the main delivery methods. Loyalty programs, product comparison, accounts with order history and complex promotions are easier to add once you have data on how real customers behave.
A marketplace gives you a ready stream of buyers, but you pay for it: a commission on every sale, logistics costs and paid promotion inside the platform. The rules change without asking sellers, and your price is effectively set by competition with the listings next to yours.
Your own online store works differently. You control the price, the presentation and the range, you get customer contacts and can sell to them again through email and remarketing. In return, you have to attract traffic yourself through search, search ads and shopping ads.
That is why most sellers end up running both channels. The marketplace brings volume and new customers; your own site brings margin, a loyal audience and independence from a single platform. Technically, this comes down to a shared product database: stock and prices stay in sync, and the catalog is sent to the platforms through a feed.
Most search traffic to a store lands not on the home page but on category and product pages, through queries like men's running shoes size 10. Preparing for promotion starts when the catalog is being designed.
If none of this is built in when the online store is created, the SEO specialist will have to start by restructuring the catalog, which takes longer and costs more than getting it right the first time.