About 10-15 of the 25# bags, depending on your definition of "a good few inches."
The main reason to use shavings is if there are financial concerns, or if you want the bottom of your coop to have some padding or insulation. See the post just 2 before yours.
If you want to find your nearest retail outlet, or want to find a distributor for your local feed store to special order it for you, you can call the company at 800-367-1534. They are in Spokane, WA, so they're on PST.
I live in western WA, and have had an impossible time finding this product. I was finally able to get a 25 lb bag online from here: http://www.horse.com/item/sweet-pdz-stall-freshener/SLT311771/. When I first clicked on this site I was offered a $10 discount plus free shipping for anything...
I have both chickens and turkeys. The turkeys seem to eat everything, including their shavings. So far it hasn't caused any problems, but I worry about them getting an intestinal or crop blockage. Does anyone have a problem with their birds eating the Sweet PDZ? Is it likely to cause any...