The short answer: a template-based marketing site runs $1.5K–$5K, a custom-designed brand site $5K–$20K, and serious e-commerce $10K–$50K+. The spread isn't about pages, it's about thinking. A $300 site reuses someone else's thinking; a $15K site builds yours.
Three things actually drive cost: strategy (who lands here, and what should they do next?), custom design (does it look like your brand or like a theme demo?), and engineering quality (does it load in under 2.5 seconds and pass Core Web Vitals, which directly affect Google rankings?).
Where brands waste money: paying agency prices for an unedited template, rebuilding the site every two years instead of iterating, and skipping conversion tracking, so nobody ever learns what the site earns. A website isn't a brochure; it's a salesperson. Pay for one that closes.