Cistern's One-Time Dollar Price for Storage Capacity calculates the price of the storage container (or what is reffered to as a "cistern") per gallon of rainwater saved.
A tank holds 1,420 gallons of water, and would cost around $1500 to purchase and install.
$1,500 ÷ 1,420 gal = $1.06/gal
$1.06/gal = price of storage capacity