One thing Ella forgot to mention in her excellent post was the cost of patenting the product.
For example Retention+ is patented technology. This means that the formula is protected and can not be copied. People can colour their monomer purple but it is nowhere near the same. Creative by the way was the first company to have a colour enhanced monomer ... then lots copied, but colour is just colour, the formula is protected by a wide margin and that costs 'pennies' too.
You do get what you pay for by and large.