Installing a complete rainwater catchment system can cost as much as $8,000 and $10,000 for a single family home.
The major cost is in the tank and install and depends on the size of tank you have installed or the size of rain water catchment tank you install.
You can sometimes do the rain water catchment system install yourself and save money which will make it cheaper but it requires some work.
It takes many years to see the return on the investment of a rain water catchment system but it should last for many years after it's paid for itself.
I would highly recommend having a pro install the rain water catchment system to get it done correctly and save aggravation.
However if you know how to install the rain water catchment system yourself you can likely save some money and have something to do in the process.
It can be a great learning experience as well.