That's like asking how much does a car cost?
It depends entirely on
1) Project Scope
2) Dynamic or Static
3) Custom or Cookie cutter
4) Bells & Whistles
4) Expertise of the design/developer team
5) Regional economy
It veries wildly. I mean really really wildly. You could find a highschool kid who charges $20 an hour, or a design agency that charges $200/hr or more. A simple five page site could take 15 hours, where as something like Facebook could easily take 5,000 hours. I live in Detroit, and we had our city website designed by a fancy firm at one point. The tab on that was over one million.
If you are just starting to develop websites then the best thing is
to charge a fixed fee of say £250 (this is UK pounds because I live in UK) for basic
5 pages website that requires no scripts of any types or
creating images of any kind.
The idea is to create a portfolio of clients which you can showcase on your site to attract more clients.
There is truly no such thing as a basic to medium website.