What decides the cost?
The biggest factors are scope, number of unique page layouts, content requirements, eCommerce or portal functionality, integrations, admin controls, performance expectations, security requirements and post-launch support. A five-page brochure website and a role-based customer portal are fundamentally different projects.
Ask for scope, not only a number
A useful quotation should state what is included, what is excluded, how many revisions are included, who supplies the content, what hosting is required, what integrations are part of the build and what happens after launch.
Budget for ownership
Domain renewal, hosting, backups, maintenance, email and occasional content updates are part of operating a website. Planning these from the start usually costs less than emergency recovery later.