try your local landscaping place. It's dirt cheap when you need large amounts of rock, especially if you compare it to petsmart, ect. They charge $20 for a less-then-medium sized rock, when your landscaping place would charge .30 a lb (or something to the effect). Plus there would be a large variety to choose from, and you're getting something completely unique, not mass produced. Just make sure it's not a limestone based rock, a simple drop of vinegar will tell you that if you're unsure.