I don't think there is much difference between cheap or expensive products at all. If something is harsh, you can dilute it 10 to 1. I have heard that the latest version of Suave shampoos, I think it's called Salon, is really good. I buy something really inexpensive at the drugstore and always dilute it. I used Dr. Bronner's for years, and other very mild shampoos from health food stores, and agree with the poster here who said that a surfactant is a surfactant is a surfactant. The pricier brands are not selling more effective or gentler surfactants.
Hard water is another problem and like various people here have said, to remedy it you need to install a softener. Water filters remove impurities but do nothing to soften water. And softeners are another set of issues and not cheap, but definitely worth it for many. If your area has hard water I'd ask other people in the community how they remedy it, and if there is a good local softener installer they recommend. There are new magnetic softeners which may or may not work ... it's hard to get a realistic appraisal but if you look on amazon or google around you'll see them. In France they sell magnetic softeners which attach to the faucet or shower-head, and I've used these and think they do a good job though a softener would be better.