I don't recall exactly what I paid, and it would have been a decade ago.

I cut mine into an L shape with wire cutters. These things readily break (they wanna break), but it was easy to do and I cleaned up the sharp pieces with pliers.

As I say, none of my five cats ever minded it.

I have a theory about the spacing... I think it was wide enough that it flexed the cat's paws, causing the gravel to fall out. I think if it supported the paw too well, the bits would stay between their toes.