Do they have just a regular feed store nearby? Tractor Supply around here has the 25 pound bags of Manna Pro granite for $9 bux, but since I used to raise ducks, I know that a regular feed mill or feed store will probably have grit cheaper, the two closest to me have 50 lb bags of grit for 4 to 5 dollars, its locally sourced and crushed, so theres no added cost for shipping heavy bags. The one feed store sells a crushed granite thats a nice mottled grey, the other has a light colored crushed quartz. If my natural forest souced and free pea gravel and woods compost mix doesnt work in the long run, 5 bux for 50 lbs of nice grit works for me! Just be careful to ask what type of stone they crush, some areas south of here crush limestone as grit (which may not be a bad thing) but it will raise soil ph.