The cost of a website design varies significantly by the size of the website, required functionality, integrations, and level of customization. This is why creative agencies typically offer a quote for website design instead of having a set-price list.
Huge websites take longer to migrate and require a more elaborate menu structure than minimalist sites, therefore, requiring more massive investment. The amount of functionality required for your website also affects the price. Features like an online store, blogging, event registration, forms, user permissions, private pages, interactive maps etc. will all be taken into consideration for a web design quote.
The same can be said for API integration; if you want to connect your customer relationship management (CRM) system or marketing software to your website, there may be a setup fee.