Sand-blasting cabinets?

So where do all you guys get your blasting grit from? The boxes of beads/grit sold at Harbor Freight are so expensive, ~$50 if I remember correctly, I just can't bring myself to cough up the coin for it. C'mon, sand is supposed to be cheap.

I've used good quality playground sand, as well as silica sand in my HarborFreight floor cabinet. (Yeah, I know the health hazards associated with silica dust). These work pretty good as long as I use a bit of window-screen in a frame to screen out the big chunks as I pour the sand into the hopper.