It’s as much as you want it to be. From $400 to $6,000, there’s a system for every wallet and every level of “hard water frustration.”
My advice? Start with a water test (free at most hardware stores). Then imagine a life without chalky glasses. Isn’t that worth a few hundred bucks?
Buy the best you can afford. Your future self—lounging in a bubble bath with ridiculously soft hair—will high-five you.