There is no way to put a figure on the price of website straight away. The cost can vary from a few pounds a month to thousands depending on what is to be achieved by the site, the size and complexity of it and the company you use. There are companies out there that offer websites for as little as £10 per month, but if you really want a website that is going to attract customers and give you the flexibility then these are not for you. You do often get what you pay for in terms of website design and therefore do not always be tempted to go with the cheapest.
You need to know exactly what you are being quoted for and therefore may need to spend a bit of time researching certain terms such as Search Engine Optimisation or off-site Link Building. Once you have a few quotes, do not be scared to ask if you are unsure what something is after all you will be paying for it so need to have and overview of what you can expect to get from the end result.