I have a centralized water purification system in my house and I also have a centralized water softner unit (since we have hard water in our area).
We have a Culligan system which is one of the priciest ones out there. There are others (GE makes one and so do a lot of other mom and pop companies).
We went with Culligan because my husband years ago was an engineer there and knows it's ins and outs and quality and would not be satisfied with anything else
. You can look at GE for example and save some money. To me they are all the same
Our system cost us thousands of dollars (not sure the exact but it was definitely 3K or more)