Much as any other form of advertising it is difficult to fix an exact cost of a website, it depends on the needs of the client and what kind of site is required. ECommerce sites are relatively complex to create and are usually bespoke, so these can become quite expensive. However, may businesses simply require an online brochure site (like this one) and these are quite inexpensive to start up, typically you can expect to pay around £300-500 to have one set up including the purchase of a domain name e.g. southbucks.net, graziemille.co.uk etc.
If you would like to discuss your requirements with me either call me on 01494 862484 or use the email form and I will call you back (standard UK landlines only).