These medicines aren’t priced this high because they are expensive to manufacture. For example, giant drug corporation Gilead charge the NHS £39,000 for a hepatitis medicine (ledipasvir-sofosbuvir) that is made and sold for a profit in other countries for less than £500. Many of the cancer medicines we use can be made for a tiny fraction of the price drug companies charge the NHS.
So why are we paying so much? The reason the drug companies can get away with charging sky-high prices is because they have been given a monopoly by the government - they are the only ones who can make and sell the medicine in the UK. These monopolies are created when a drug is granted a patent by the government. This monopoly prevents the competition that would drive down the price. Drug companies are able to get away with charging as high a price as they like and as a result are the most profitable industry in the world.
Patents are given out by the government to people who have created useful inventions. They prevent others from making, selling or using the invention for 20 years. They are supposed to encourage innovation but in reality they cause huge problems. They lead to prices so high that medicines are rationed and people die without access. And as there are little profits to be made selling medicine to poor people, diseases that kill millions around the world every year are ignored.