The cost of a website is determined by what functionality you want your website to have. Will you be supplying all the images or must the designer do that themselves? I have always had this problem with cost, because some designers charge a once of fee for a 5 page website, but they do not mention what functionality is included and then you get designers that charge by the hour. But if you are a better designer, then you will do the work faster, in less hours I mean, compared to the designer that just finished with college, that will take more hours to get to the same result. So that has always been a catch 22 for me. I rather suggest that you submit a clear outline of your requirements and let the designer give you a cost of a finished product. The other thing is, that you don't always know what functionality you want, because you don't know what is available, so ask your website designer for some advice on what functionality they can offer for your website and the costs involved and then you can decide if it is worth it or not.
Very important with regards to cost. Be as specific as possible when requesting a quote and once you have received the quote, make sure that all your requirements are outlined, as you do not want to pay hidden fees at a later stage.