Never in a million years would I pay that for an operating system. But then, I wouldn't use Windows either.
I see Microsoft never fail to rip off British customers. Take a look and see what it costs in the US by comparison - $39.99 maybe? There was even some talk about the upgrade edition (which is what you're referring to) being $14.99 for a limited time. Whether that will happen or not, I've no idea.
You could use Ubuntu and have a far more advanced system for free.
I thought an upgrade from Win 7 to Win 8 was to cost about £25. However, if you are using Win 7 and are not bothered about touch screens, then I don't see ant compelling reason to change from Win 7 although I expect we will be told that it is more secure !