Well, as already mentioned, there's no one-size-fits-all when it comes to website development.
What if you only need a static 5 page professional looking website?.
Or maybe you need a database backed, php driven enterprise website that tracks multiple items/variables from different branches?.
Also, does the client have a well rounded corporate image/brand? if not, will it also be created from scratch? adjusted?.
As an example, a while back I needed to develop a very specific website. Think Auto Classifieds (not really, but close). I bought a ready-made system as a base. The developer's license was $600.00 (way cheaper than developing from scratch). After all functionality was added, tweaked and/or optimized, and design re-worked, the whole thing ran about $7000.00. Still well below the client's budget.
Does it mean a professional website runs $7K? no. But it did in this instance. You can go way higher, or you can go lower.
You can get a professional-looking website from $50-$150, no doubt. It all boils down to the specific needs for the project.