The amazon.com Petco link, they have the 25 qt bag on sale. $13.99 and shipping is $5.99- for as many bags as you order. I ordered three and shipping was $5.99 total.
About $.50 per pound to your door, and the Zilla stuff is fine enough I have no trouble at all with clumping and blocking flash holes or getting stuck in 223 bottlenecks.
I like it way better than stainless steel pins, and after building a couple wet SS pin tumblers, I'd much rather use the walnut + NuFinish + odorless mineral spirits + torn dryer sheets- any day.
The SS pins get stuck in the cases and in the flash holes, and then you have to rinse and dry and hope all the pins came out... Built a rack to let the pins rinse out. Still had pins stuck, two SS pins together wedge nicely in a flash hole. Lots of work for no real gain IMHO. I am junking my SS tumblers and pins. What a bad idea.