My brain hurts. If a ball that costs $20 and lasts 30 years is too expensive, then a ball that costs $2.50 and lasts a day is also too expensive. This is not a difficult math problem.
* What happens when they get wet? Does it get a lot of mold?
* What happens during a flood?
* How fast the surface wears away?
* What happens when a dog bites it?
* Does the dirt accumulate inside and make the ball heavier?
It's looks like an interesting idea, but the 30 years claim is a little optimistic.