At Farm & Fleet in Waukesha, Wisconsin, I just bought a 50 pound bag of the same type of grit for $8.39...the little rocks seem so big, but the bag is the #2 size that says on the back is right for the age of our birds. I think it says "cherry stone" on the front, and it is granite also.
I used grit paper in the brooder starting from day one that you can get at
Walmart for $2.87...it was doubly great for the chicks because it was a good walking surface for them as well. My next little group of chicks will be here in a couple months and I will use that grit paper again-it was awesome!
As far as your grit question, I hope other people respond, because I have always wondered if everyone uses grit, and if they do, what kind or size. My farmer neighbor says to just grab a handful of gravel off the side of the road every now and then and toss it in there...
(hmmmmmm, I wonder if sand would work......this is my first experience with any kind of birds, so don't laugh at me if that sounds really stupid!)