This is probably the most commonly asked question within the web industry, but why? In this article and others related (links below), I'll shed a little light into my 16+ years as a web professional and the practises I've commonly seen.
So... to reply to your question ‘How much does a website cost?’. The truth is that it depends on a lot of factors. You could think of it like saying, how much does a house cost? How much does a renovation cost? Or how much does a car cost? The defining ingredient in all of these items really is the scope, or in other words, what’s included and the quality of the final product.
So the logical next question - what's the scope of a website? Well that depends on how large the website is and to what level of quality it is created. Homes come from units to mansions, cars range from small hatchbacks to V12 supercars, and websites range from 1 to 100+ pages with varying levels of detail as to the design, content, functionality and development.
In short, a small one page microsite may hover around the ~$2,000 mark for professional production. Medium to large sites will typically range within ~$5,000 - $50,000+ depending on the scope. In all cases, these should include original design and development, meaning no third party templates (which commonly isn't the case, see related article)!