Bob,
I used a “First Alert” kit I bought in Lowes for about $15. It includes the cost of the Laboratory analysis and report. I believe the kit you buy in Home Depot entails an extra cost for the laboratory analysis. Quite a few residents have used the First Alert kit.
The cost for correction varies widely. Some people paid up to a $1000 to have it done by an outside professional. Pat Pannese bought the necessary parts and installed his own for about $150. He said it was real easy. Other residents have also installed their own.