Content and complexity. E-commerce websites generally require many products to be configured and entered into the website. All images have to be resized to allow for quick loading of pages to increase visitor satisfaction. Many times have variable products with different sizes, colors and such much be configured. This can become quite complex. Then there are shipping system integrations such as FedEx, UPS, USPS and more. Additional options liking booking systems for service businesses, hotels and the like require specialized plugins that increase the cost.
So many things go into having a smart e-commerce site that we will consult with a client to understand their particular needs before giving them a quote to have the website they’re looking to have built.