The short answer
Every credible answer starts with scope. The same brief delivered to five studios produces five different figures because the underlying assumptions — page count, design depth, content ownership, integrations and languages — are rarely identical.
What actually drives the number
Design complexity and functional requirements dominate. Bespoke layouts, animation, custom components, data-driven pages, multilingual architecture and third-party integrations each add design, engineering and testing effort that page-count pricing cannot express.
Where budgets are usually lost
Unclear scope, late content, and functionality added after development begins. Fixing an architectural decision after build is consistently more expensive than resolving it during discovery.
A practical way to decide
Define the commercial outcome first, then the smallest scope that can achieve it. Build for the next eighteen months rather than a hypothetical future, and keep the architecture open enough to extend.
What BH recommends
Start with a scoped discovery. A defined project scope, investment and target delivery schedule before development begins is the single most reliable way to keep a web project predictable.