Stormwater Management Costs in Atlanta, Roswell, and Hapeville

We are working on a project for one of these cities. All the stormwater management requirements are about the same for these cities: green roofs, permeable pavement, retention ponds, or rainwater harvesting. The owner wants to redo a driveway, so they were thinking pervious paver bricks. Let's look at a cost comparison vs. rainwater harvesting:

These pavers are the only ones we could find for sale on the internet. They look nice; I might buy them for myself when it's time to replace my driveway. But the owner is concerned about high heels getting stuck in the spaces. And let's compare prices:

1 paver is $28, and covers 32 square INCHES. So you need 4½ to cover a square foot.  That's $125/square foot!

By comparison, an above-ground corrugated steel tank, with the pump and controls necessary to integrate with an irrigation system can be found on the internet for an average of. . .   $1.12/ square foot.

A below-ground steel tank, costs a little more than above-ground, and installation is more. Maybe $3/gallon, installed.

Sure, there's a cost for the space for an above-ground tank. And if you don't already have an irrigation system, you'll need to add that cost. And Home Depot doesn't always have the lowest prices when buying large quantities. But still, $125 vs. $1.12 or $3???

UPDATE:  Received some immediate feedback on this blog entry. Pervious pavers on commercial jobs are available for $8 - 18/square foot. Still, rainwater harvesting is much, much less expensive.