pH, iron, turbidity, co2... all should be addressed. The real question is what quality of water do you want and what is your budget and ability to maintain equipment? Are you a DIY'r? Or are you needing someone to do the work? A simple solution that is marginally effective may be fairly cheap. Proper treatment will obviously be a bit more expensive. Some people want to fix their water for under $100, this is simply not going to happen. Others have a huge budget and love toys, the best of everything and they want near perfect water.