How long is a piece of string? Not something you want to hear when budgeting for a new website but if you have not put thought into why you actually want a new website this could be the answer you receive.
Websites are often the first point of contact your prospects have with you and is therefore one of the most important mechanisms for future growth, but you need to think deeper into what you want your website to achieve. This in turn will help you budget as you are then able to give the Web Developer enough information to give an honest quotation.
How much functionality do you really need? Bells and whistles look great but it all costs money. Yes it is extra work to add on an e-commerce facility and yes a customer portal will cost more so think carefully about what your company really needs to succeed. Plan from the start and remain focused on your core objectives.
Another common stumbling block is page content. Companies often allot members of staff, often from the technical department, to work on text but the reality is that copywriting is a skill and it is not a five minute job to knock up a web page. They soon find that a technical description of their latest service is not sales focused enough to appeal to their target audience and this often leads to significant delays or devalues the overall website.
How much design and customisation is really the million dollar question as this really affects cost. If you are happy to use existing layouts and will not be tempted to tinker then pre-designed themes will save you a fortune. But be realistic, if you have your heart set on specific detail then you definitely need to go down the bespoke route.