1: £79.99 is £66 before tax.
2: That "piece of metal" is called copper, it is not a cheap metal.
3: Depending on the block chosen it also has acetyl or perspex on it.
4: A lot of research and development have gone into it.
5: The CAM/CNC equipment that makes them was/is not cheap to buy/maintain.
6: The blocks are tested before being packaged/shipped to ensure they work properly.
7: They come from Slovenia, that's over 1000 miles away.
All in all I think £66 before tax is fantastic for what you get, but then I'm not an idiot so I looked at all the facts before forming my opinion.