First you need to decide what type of web site you want to build. First one is Personal Web site that may be your family web site and can have the maximum of 15 pages. And second is the Company Web Site that can have the maximum of about 30 pages. Again you should tell if you want to build your site in the already designed template, so development time and cost of the web site will be more and more less, similarly, If you need extra sunique design where some animations playing on the top of every pages and extra good buttons, just like my web site header image, as a result development time increases and so cost will be higher as compared to previous one.   

Company web site include mainly two type of sites one is Static another is dynamic. For the case of static above listed cost is applicable. For Dynamic sites, wide range of tools are available. Those are basically server side scripting Technology. Mainly there are Microsoft ASP, Sun JSP, CGI and PHP. You can choose any one of these. Sites based on these technology will have comment, suggestion or feedback facility for customers, guest book facility and much more based on your requirement. Cost of these site will be determined on the basis of the requirement of web sites.