On price difference, the salon and supermarket shampoos and conditioners were pretty much the same, even though a supermarket shampoo was about the fifth of the price of a salon shampoo, you only need to use about a fifth as much due to the concentration.
The main ingredient in most products is water, but salon versions use a small percentage in the overall product. This is why you will use a much smaller amount of the salon product.
When it comes to quality of a product, the salon version contains much higher concentrates of the right active ingredients. These are the parts that will do the most good for your hair, the main ingredients are sulphates, which are the cleanser and foaming agents. Salon shampoo s contain higher quality sulphates and some are sulphate free. Cheaper, lower quality sulphates can cause colour fade if they are too harsh and can be found in higher concentrates in supermarket shampoos.
If you're tempted by supermarket shampoos and conditioners with big names such as L'oreal or Herbal Essences, bear in mind that these are cheaper because of the lower quality of ingredients and the lack of concentration and higher water content.
If you use cheaper shampoos and conditioners, you will probably experience build-up after a while, making your hair dull and less easy to style.
As a last thought, if supermarket brands were as good as salon versions, wouldn't salons be using the cheaper supermarket brands too?