Very little!
First, you need to create the site on your own PC. You've probably already got some suitable software, otherwise you can get WebPlus 6.0 free, here:
http://www.freeserifsoftware.com/
Then you need some web space to host your site. You've almost certainly got some available for you to use, free of charge, because virtually every ISP provides free space for their customers.
When you upload your site to your ISP's server, it will have an address like www.myisp.com/users/char_1990 but there's no need for you to use that address.
Next, you need to 'buy' a domain name. (Actually, domain names aren't really 'bought'; you effectively rent them).
A firm like UKHosts.com can provide you with a .co.uk domain for �5 (+VAT) per year but there's a minimum period of 2 years. (So that's a minimum of �11.75 that you've got to pay).
You can set things up so that when users type in www.char_1990.co.uk (or whatever other name you've chosen) they're redirected to view your site on your ISP's server. However, when your home page loads in their browser, the address will change to show the real location of the site. This is acceptable to some people but it looks very unprofessional for commercial sites. If you want the .co.uk address to remain in the browser's address bar, you need to use 'cloaking'. UKHosts.com offer this service for just �2 (+VAT) per year.
So, assuming that you've got some software and that your ISP offers free web space, you can have a .co.uk site up and running (including domain name cloaking) for �7 (+VAT) per year. Since there's a minimum 2 year commitment, that makes a total payment of �16.45 (inc VAT).
I've chosen UKHosts.com for my examples simply because their prices came quickly to hand . I've seen other firms offering .co.uk domain names for as litt