Supermarket shampoo & conditioners are full of chemicals that are no good for your hair long term. Yes, it'll feel lovely at the time, but it really is damaging your hair. A hairdresser can tell if you're using a cheap shampoo & condition, especially when they go to colour your hair. The colour may not hold if you're using cheap stuff in it. I love my hair, so I don't mind paying that little bit extra for it to be healthy. FWIW, my shampoo & condition will usually last 6-9 months, which is from my hairdressers.