These are extremely expensive in the shops. I know you can get them from ebay but mostly on bidding items. Is there online pharmacy websites that sell these blades at a reasonable price?
Where do you get them from where it doesnt cost the earth?
If you've got a local market, you might try there. I managed to get some for my husband recently that were a lot cheaper than Tesco etc just because they were sold out of the usual packaging. Good luck!
These are so expensive because they are the most stolen item from shops. Their cost is high because you are paying for the stolen items too. Buying them from a car boot is a guaranteed way of knowing you are getting stolen goods.