I buy Aldi shampoo and conditioner, one of my children has hair down to her bottom and it is lovely and shiny using this stuff (probably wont help your flaky scalp though).
I've bought some E45 shampoo for dry scalp, not cheap. I can't say I have dandruff but my hair is very dry at the mo and my head itches. Just hope I'm not allergic to my usual shampoo and hair mousse.