I don't think you can buy it outright. You register it and registering isn't owning, it's kind of like renting it. So long as you renew it every couple of years, you have the right to keep it. As for price they aren't expensive and quite a few people buy more than one for their site. The last site I did, the chap went for his_name.co.uk and his_name.com. I think that it was less than £15 a year for both. I don't know where I got that number from but it just sounds right. Truth is, I'm not sure if I can remember!
PS asking about hosting is well, not really helpful. Have a look at the .net magazine forum and maybe read the mag. They have a list of hosting companies with a checklist of services you can compare. You need to think about what you want from your site too. For instance, if you have just the basic requirements I think you can still get free hosting. If you want all-singind all-dancing, heavy traffic, secure, ecommerce.... that'll cost you and you need to do much more research. I remember asking the same question when I hosted my first site. You can always find as many people on line to slag something off as you can to recommend it!
godaddy.com (do not host with them !) but the price is good for registering domain names.
Look for a local host in the UK, though it doesn't matter where the site is hosted, as long as you can get support when you need it
Just remember, with hosting, often times, you get what you pay for!
A site for checking out reputations on hosting companies:
Personally, I use and have no problems with:
http://www.gowesthosting.com/ (moved a heap of sites to this company a little while ago and they were very helpful).
http://crystaltech.com/ (have since been taken over by another company, so may move the sites from here to the above company as well - as I get a lot more space allocation for a better price).
I've also heard good things about:
I use from last two years https://nextpointhost.com/ like hosting company and place from where to buy my domains. They are not very cheap, but are very reliable. Very useful thing is that they provide free domain ID protection for which all other companies want money.