£2,500 is the entry point, and stores reach it less often than brochure sites do. That floor covers a focused catalogue, a custom theme, the category structure, product markup, a payment gateway and the launch search work.
Catalogue size is the first thing that moves it, though not in the way people expect. A thousand products imported cleanly from a spreadsheet costs less to build than eighty products with inconsistent data, missing images and three ways of recording a size. Beyond that, the additions with real build time in them are a migration off an existing platform, multi-currency, a subscription or trade-account tier, and a connection into stock or accounting software.
Search on a store is a longer job than on a brochure site, because there are hundreds of pages to earn rather than a handful. Some retailers begin an ecommerce SEO retainer at launch and others wait a quarter to see what the new structure picks up unaided. Tell us your product count and current platform on a call and we will price it. The tiers are published if you want the shape first.